Low data volume satellite communication system

ABSTRACT

Systems are disclosed for a communication system optimized for low data volume communications. In embodiments of the invention, a terminal in the communication system is configured to receive beam shape information from a satellite and use the beam shape information for calculating the terminal&#39;s initial transmit power based on the beam shape information. The terminal can also determine the terminal&#39;s location and calculate an achievable information data rate of transmitted bursts based on the beam shape information. The terminal can also determine an estimated terminal position based on correlating signal-to-noise ratio measurements on the camped beam and at least one neighbor beam neighboring the camped beam.

BACKGROUND

The present invention relates generally to the field of satellitecommunication systems. More specifically, the present invention relatesto embodiments of satellite communication systems suited to low datavolume communications.

A conventional Mobile Satellite System (MSS) can be configured toprovide services, such as voice and packet data communication throughoutthe world. Referring now to FIG. 1, a typical MSS 100 comprises one ormore geostationary satellites 102, one or more Gateway Stations (GS)104, and one or more Satellite Terminals (ST) 106. The STs 106 caninclude mobile terminals (handsets), vehicle terminals, and/or fixedterminals. The GS 104 can be configured with external interfaces toexisting fixed telecommunication infrastructure as well as to thewireless telecommunication infrastructure. For example, a GS 104 mayinterface to a Public Switched Telephone Network (PSTN) 108. Thesubsystems in Gateways can be oriented to various types of transmissionfunctionality, e.g., circuit-switched or packet-switched. The names ofthe subsystems vary between implementations. The term for all theground-based subsystems is Network Infrastructure 110, which includesthe GS and PSTN subsystems in FIG. 1. The satellite directs energy inthe forward link to areas on the ground called beams 112. The sameconcept of beam-forming is applied in the return link to separatelycapture the signals from terminals in each beam at the satellite.

Information is communicated in finite duration transmissions calledbursts. Bursts are composed of: waveforms related to physical layerfunctions such as detection and synchronization (e.g., pilot signals);and waveforms that contain modulated data. The modulated data includespayload fields and error detection fields (e.g., CRC). The payloadfields may contain control information (such as terminal identity), andapplication-related information. Any payload information that is notapplication-related is defined as an overhead.

Information can be transmitted via these satellites 102 using a CommonAir Interface (CAI). Existing satellite CAIs typically concentrate onefficient operation for relatively large quantities of data. Forexample, a voice call lasting one minute might involve 30 kB(kilo-Bytes) or more of information transmission in each direction.Packet data operations often involve even larger quantities of data,frequently in the MB (Mega-Byte) range. Providing a connection in aconventional MSS typically involves a sequence of steps including:

-   -   Requesting and establishing a link between a ST and network        infrastructure via a satellite;    -   Exchanging information characterizing the capabilities of the        end points;    -   Exchanging information describing the objectives and        configuration of the connection;    -   Transmitting the data and related acknowledgements; and    -   Exchanging information to terminate the connection.

Prior to transferring information, a ST 106 typically must “register”with the network. In addition, the ST 106 typically must “re-register”when it moves from one satellite beam to another. When a ST isregistered, the network infrastructure is aware that the ST is presentand the beam within which that ST can be located. After a ST isregistered, data exchanges can proceed. A conventional MSS data exchangemay start with establishing a communication channel. This may includesending a Random Access Channel (RACH) burst from a ST 106 to asatellite 102, which passes the RACH burst to a gateway 104. The RACHburst might include source information, such as a called party, terminalidentity (ID), terminal capabilities, the message intent (such asestablishing a packet connection) and possibly location information.Next an Access Grant Channel (AGCH) burst may be sent from the gateway104 to the ST 106 to establish a bidirectional traffic channel forfurther exchange of information. A typical AGCH burst can provide otherinformation, such as an indication of available resources for the ST106. Security information may be exchanged back and forth between thegateway 104 and ST 106. Further capability information, such as maximumdata rate, may also be exchanged between the gateway 104 and ST 106.

After a communication channel is established, data may be sent betweenthe ST 106, satellite 102, and gateway 104. The data may be sent inmultiple messages. Each message includes header and protocol overhead,which will vary in quantity depending on the scenario, and can amount toapproximately 20% of the message. Acknowledgement messages (ACK) arealso sent to acknowledge the successful receipt of the data messages.If, the data messages are not successfully received, aNon-Acknowledgement message (NACK) is sent and the data message(s) areresent.

After data communications are complete, the ST 106 will send a “done”message to the satellite 102 which gets passed on to the gateway 104and, if the “done” message is successfully received, a terminationmessage is sent to the ST 106 acknowledging receipt of the “done”message. For large quantities of data, the exchanges other than“transmitting the data”, can correspond to a reasonable overhead.However, for smaller data exchanges, the overhead can significantlyimpact efficiency.

U.S. Pat. No. 10,193,616 (which is incorporated herein by reference)discloses a satellite communication system which is configured forapplications which exchange a comparably low volume of data between theterminals and network infrastructure. In this system, much of theoverhead associated with communications between terminals and networkinfrastructure is eliminated by configuring the terminals to transmitinformation in prescheduled bursts that are intended to communicate acomplete message. In this manner, the overhead associated withestablishing and terminating a connection between a terminal and networkinfrastructure is eliminated making the system much more efficient.

Power control can be used for adjusting the signal quality at areceiver. Performance of a system (e.g., its capacity at given errorrates) improves when the Signal-to-Noise Ratio (SNR) at the receivers isclose to a threshold for all transmissions. When supporting sporadictransmission of small quantities of data, the design of power, timing,and frequency control can have different sensitivities to propagationand environmental conditions than those associated with more continuousmodes of transmission.

In a conventional satellite communications system, power is adjustedbased on on-going transmissions from a terminal. For example, thenetwork may command an adjustment to a terminal's transmit power inresponse to each burst received. Power control is often applied in bothdirections (to and from a terminal). For satellite links using codedivision (i.e., simultaneous transmission with spread sequences) theterminal transmissions represent the more challenging direction forcontrol. That is, simultaneous transmissions from a satellite to aterminal experience almost identical propagation conditions (e.g.,fading and shadowing). In contrast, for the direction from multiplesimultaneously transmitting terminals to a satellite, the propagationconditions are typically different for each signal. For the case oflarge numbers of near-continuously transmitted bursts, power controlperformance can be dominated by the on-going feedback that sets powerbased on recent experience. Errors in the initial transmission may belarger than average, but their impact is reduced in significance as morebursts are transmitted during a connection.

In systems, like those disclosed in U.S. Pat. No. 10,193,616, whichcommunicate using a small number of bursts (typically only one burst),power control performance can be dominated by the ability of terminalsto set the initial burst power accurately. Common power control methodsused in conventional systems which utilize on-going feedback are notparticularly well suited for applications which communicate using asingle or very few bursts to communicate data. As such, a need existsfor new power control methods which can more accurately set the initialburst power of a satellite terminal.

SUMMARY OF THE INVENTION

One embodiment of the invention relates to a communication system,comprising at least one terminal; at least one satellite which creates abeam having a beam shape that enables communication with the terminalwhen the terminal is located inside the beam, at least one networkinfrastructure in wireless communication with the terminal, the networkinfrastructure having an information element which includes beam shapeinformation representing the beam shape. The terminal receives theinformation element from the network infrastructure and calculates theterminal's initial transmit power based on the beam shape information.The information element can also include scheduled transmissioninformation that the terminal uses to communicate with the networkinfrastructure by sending a burst comprising a message at apre-scheduled time such that the network infrastructure can derive theterminal identity by comparing the time of the burst with the scheduledtransmission information in the information element without having toinclude terminal identity information in the message.

The beam shape information can describe the beam shape in terms of gainas a function of spatial location formed by a transmitter of thesatellite, gain as a function of spatial location formed by a receiverof the satellite, gain differences between a transmitter and receiver ofthe satellite as a function of spatial location, or any number of otherways. The beam shape can have a cross section corresponding to a definedfunction such as a sinc function. The terminal can be configured todetermine an estimated terminal position based on the beam shapeinformation or based on correlating signal-to-noise ratio measurementson the beam and at least one neighbor beam neighboring the beam. Theterminal can also be configured to calculate an achievable informationdata rate of transmitted bursts based on the beam shape information.

In another embodiment of the invention, the communication system cancomprise a terminal; a satellite which creates a beams having beamshapes, the beams including a camped beam and at least one neighboringbeam which neighbors the camped beam, the camped beam enablingcommunication with the terminal when the terminal is located inside thecamped beam such that the satellite communicates with the terminal usinga forward link and the terminal communicates with the satellite using areverse link. Network infrastructure is in wireless communication withthe satellite and the terminal, the network infrastructure having aninformation element which is sent to the satellite and which isbroadcast by the satellite along with system information, theinformation element including scheduled transmission information andbeam shape information representing the beam shapes. The terminal isconfigured to wake up at a pre-scheduled time, obtain the informationelement by reading the system information broadcast by the satellite,obtain a signal-to-noise ratio for the camped beam and at least oneneighboring beam from correlations that arise during acquisition, derivea location estimate of the terminal by matching the obtainedsignal-to-noise ratio for the camped beam and the at least oneneighboring beam with the beam shape information. determine a reverselink transmit power for the terminal based on the beam shapeinformation, determine an information data rate for the terminal basedon a threshold signal-to-noise ratio for the reverse link, andcommunicate with the network infrastructure by sending a burst at thedetermined reverse link transmit power and information data rate. Thecommunication can be structured as a message at a pre-scheduled timesuch that the network infrastructure can derive the terminal's identityby comparing the time of the burst with the scheduled transmissioninformation in the information element without having to includeterminal identity information in the message. The beam shape informationcan describe the beam shape in terms of gain as a function of spatiallocation formed by a transmitter of the at least one satellite, gain asa function of spatial location formed by a receiver of the at least onesatellite, gain differences between a transmitter and receiver of the atleast one satellite as a function of spatial location, or any number ofother ways. The beam shape can have a cross section that corresponds toa defined function such as a sinc function. The reverse link transmitpower calculation can be based on a variety of information such as aperceived signal-to-noise ratio of the forward link pilot signal aparameterized power increment provided by the network infrastructure, along-term estimate correcting for perceived differences in forward andreturn link gains, a parameterized value representing a gain differencebetween forward and return link gains at the satellite, or aparameterized constant providing an offset associated with a linkbudget, among other information.

Further features of the present invention, its nature and variousadvantages will be more apparent from the accompanying drawings and thefollowing detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a conventional Mobile Satellite System(MSS).

FIG. 2 is a schematic diagram of one embodiment of a satellitecommunication system according to the present invention.

FIG. 3 is a schematic diagram of another embodiment of a satellitecommunication system according to the present invention showing multiplesatellites in the communication system.

FIG. 4 is a schematic diagram of a satellite communication systemaccording to the present invention showing satellite beams formed on theEarth's surface.

FIG. 5 is schematic diagram of another embodiment of a satellitecommunication system according to the present invention showing aterrestrial hub in the satellite communication system.

FIG. 6 is a schematic diagram of another embodiment of a satellitecommunication system according to the present invention showing analternative communications arrangement with a terrestrial hub.

FIG. 7 is a schematic diagram of another embodiment of a satellitecommunication system according to the present invention showing asatellite relay in the satellite communication system.

FIG. 8 is a schematic diagram showing signaling elements contained in aburst involved in a scheduled transmission according to one embodimentof the subject invention.

FIG. 9 is a schematic diagram showing modulation and acknowledgement andpower setting information for scheduled transmissions according to oneembodiment of the subject invention.

FIG. 10 is a schematic diagram showing the payload content of a BCCHburst according to one embodiment of the subject application.

FIG. 11 is a flow chart illustrating an exemplary quietening process interms of frame numbers according to one embodiment of the subjectinvention.

FIG. 12 is a schematic diagram showing the protocol associated with asuccessful scheduled transmission according to one embodiment of thesubject invention.

FIG. 13 is a schematic diagram showing several terminals in a beam whereeach terminal executes scheduled transmissions according to oneembodiment of the subject invention.

FIG. 14 is a flow chart illustrating an exemplary scheduled transmissionas seen by a terminal.

FIG. 15 is a schematic diagram showing the timing of burststransmissions from multiple terminals with scheduled transmissionsaccording to one embodiment of the subject invention.

FIG. 16 is a flow chart illustrating a terminal reading systeminformation according to one embodiment of the subject invention.

FIG. 17 is a schematic diagram showing beam characteristicparameterization for satellite communication links according to oneembodiment of the subject invention.

FIG. 18 is a schematic diagram showing factors which can be used toderive various parameter settings for the terminal according to oneembodiment of the invention.

FIG. 19 is a schematic diagram of a system showing the communicationslinks to and from the satellite according one embodiment of the subjectinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described in detailwith reference to the drawings, which are provided as illustrativeexamples so as to enable those skilled in the art to practice theinvention. Notably, the figures and examples below are not meant tolimit the scope of the present invention to a single embodiment, butother embodiments are possible by way of interchange of or combinationwith some or all of the described or illustrated elements. Whereverconvenient, the same reference numbers will be used throughout thedrawings to refer to same or like parts.

Where certain elements of these embodiments can be partially or fullyimplemented using known components, only those portions of such knowncomponents that are necessary for an understanding of the presentinvention will be described, and detailed descriptions of other portionsof such known components will be omitted so as not to obscure theinvention. In the present specification, an embodiment showing asingular component should not be considered limiting; rather, theinvention is intended to encompass other embodiments including aplurality of the same component, and vice-versa, unless explicitlystated otherwise herein. Further, the present invention encompassespresent and future known equivalents to the components referred toherein by way of illustration.

Embodiments of the subject invention can be configured to communicatesmall quantities of data much more efficiently than a conventional MSS.In one embodiment, information transmitted between terminals and networkinfrastructure is sent in bursts that are intended to communicate acomplete message without all the overhead used in establishing andterminating a connection associated with convention satellitecommunication systems. The bursts are sent in predetermined formats, atpredetermined times so that the identity of the terminal can be easilydetermined eliminating the need for much of the overhead of aconventional MSS.

As shown in FIG. 2, an exemplary low data volume satellite communicationsystem 200 can comprise at least one satellite 202, at least onesatellite terminal 208, and network infrastructure which can include atleast one ground-based satellite hub 206, and a central server 204.Communication signals can be passed in both directions between thesatellite 202 and satellite terminal 208 with uplink signals being sentfrom the satellite terminal 208 to the satellite 202 and downlinksignals being sent from the satellite 202 to the satellite terminal 208.In fact, many satellite terminals 208 may be connected via eachsatellite link. The satellite 202 can also be configured to passcommunications signals to and from the ground-based satellite hub 206and the satellite hub 206 can be configured to pass data to and from thecentral server 204.

Satellite terminals 208 may comprise communications devices capable oftransmitting information to, and receiving information from, networkinfrastructure via a satellite 202. Satellite terminals 208 may also beconfigured to communicate directly with network infrastructure as shownin FIG. 6, such as the ground-based terrestrial hub 610, using the samechannels. Downlink signals can be sent to a satellite terminal 208 usinga forward link 212 and uplink signals transmitted from the satelliteterminal 208 can be transmitted using a return link 210.

A satellite 202 can provide services across a set of channels within anarea on the surface of the earth, or above it, called a beam. Forexample, within each beam, a forward link 212 Broadcast Control Channel(BCCH) can provide system information to satellite terminals 208. Apilot channel can provide a known waveform that enables detection ofwaveforms and a reference for demodulation of other bearers. A separatepaging channel (PCH) can be used to transmit requests for connectivityto satellite terminal 208. ACK and power control channels can also betransmitted in the forward link 212 in response to bursts sent fromsatellite terminals 208. Traffic channels (TCH) can be used in both theforward 212 and return 210 links to convey payload information. A RACHcan be used by the satellite terminals 208 to request establishment of aconnection. Actual communication links can operate at different datarates. The lowest rate (which provides the highest link margin) can besupported by the most robust (or nominal) burst format.

Support for multiple networks, such as multiple satellite operators, andsupport for evolution to future networks can be included in embodimentsof the invention. In one embodiment, this support can be implementedusing the broadcast system information. The system information can beused to convey network information. As such, a terminal 208 may receivethe information needed to operate in a different or new network via thesystem information. The system information can also be used to providephysical layer flexibility in a satellite terminal 208 viasoftware-defined radio features in the satellite terminal 208. Satellitebeam shape information can also be included in the system informationwhich the terminals can use to set their initial burst transmit powerand to estimate their position. Support for multiple data rates can alsobe provided. In one embodiment, different transfer rates can beconfigured by using Walsh codes to change the length of sequences usedin information spreading, while all data rates share a commontransmission structure so they can operate simultaneously.

FIG. 3 illustrates another embodiment of the invention showing a network300 with multiple satellites 302 and 304. Satellite 302 is configured tocommunicate with multiple satellite hubs 306, 308 and multiple satelliteterminals 310, 312, 314. The satellite hubs 306, 308 are also configuredto communicate with a central server 316. The central server 316 is alsoconfigured to communicate with satellite hub 318, which is connected tosatellite 304. Satellite 304 is also connected to satellite terminal320. As can be seen, the embodiment shown in FIG. 3 consists of anetwork 300 having several hubs 306, 308, 318 and several satellites302, 304.

The communication links between satellite terminals and a satellite, forexample, satellite terminals 310, 312, 314 and satellite 302, can usemultiple sets of resources which can be characterized by a set ofparameters. For example, the parameters could define carrier frequenciesof all usable channels, chip rates, channel filtering, etc. When a fixedgroup of parameter settings is used in communication with a satellite,the associated link is termed a space relay. It is possible for multiplespace relays (with different parameter settings) to operate over asingle satellite. A set of space relays using the same parametersettings is usually termed a network. A system may contain multiplenetworks, where those networks could use different parameter settings.

As mentioned briefly above, embodiments of the invention can beconfigured to communicate small quantities of data much more efficientlythan a conventional MSS by transmitting information in prescheduledbursts that are intended to communicate a complete message without allthe overhead used in establishing and terminating a connectionassociated with conventional satellite communications systems. The bursttransmission configuration of embodiments of the subject invention,which is described in more detail below, provides enhanced transmissionefficiency for low data volume communications in a satellitecommunication system. This scheduled transmissions approach can beparticularly useful in applications with regular reporting by satelliteterminals established on a long-term basis, such as utility metering inwhich the satellite terminals monitor and report consumer utility usage.

In some embodiments of the invention, satellite terminal identities arenot transmitted but are derived at the receiver based on the time of theburst arrival. The payload portions of bursts can be used to derivetime-framing, reducing overhead such as specific synchronizationchannels. It is also possible to avoid the exchange of capabilityinformation by mapping capabilities to the satellite terminal identity.Various embodiments can include efficient rescheduling of groups oftimed transmissions to react to busy hour changes. The rescheduling oftransmissions can be done based on pre-arranged alternative scheduleswhich can be controlled via the broadcast system information. Also,power control suited to a low duty cycle and low overhead operation canbe used.

Properly setting the initial bust power can be important in embodimentsof the invention because the small data quantities exchanged in variousembodiments does not usually provide for multiple continuous monitoringand adjusting of transmission power. As described in more detail herein,open loop power control methods can be used to set the initial burstpower. The broadcast system information can be used to send theterminals beam shape information which, in turn, can be used to moreaccurately set the terminal's initial burst power. The satellite beamshape information can also be used by the terminal to estimate theterminal's position. In addition improved terminal transmit timing andtransmit frequency setting can be used to ensure that two over lappingbursts can be distinguished. These design features can be used toimprove the performance of the system such that capacity is increased,error rates are reduced, and flexibility in the use of differing datarates is enhanced.

If GPS signals are being tracked, framing can be synchronized to GPStime enabling quicker synchronization. Enhanced margin operating optionscan also be included. For example, high priority communications, such asemergency calls, can be configured for transmit-only terminals which arenot configured to receive satellite signals. Alternatively, paging torequest a special format burst transmission can be configured where thespecial format trades the quantity of information within the burst forhigher probability of detection. Higher forward link power may also beprovided in pre-defined patterns with a low duty cycle thus enablinglink-constrained terminals to receive forward link bearers at a lowrate. Various additional features of embodiments of the invention caninclude acknowledgements with low average power based on zero power ACKsas described in more detail with reference to FIG. 9 and/or terrestrialexpansion of service as described in more detail below. Terrestrialexpansion can include enabling satellite terminals to receivetransmission from satellites but to transmit to local receivers on theground enabling higher throughput for scheduled reporting, etc.Alternatively, or in addition, hub equipment can be configured toperform both transmission and reception. Frequency shifting relays canalso be used. These relays can be primarily aimed at reaching heavilyshadowed terminals such as terminals with an obstructed view of thesatellite.

One exemplary implementation of an embodiment of a burst message whichuses a robust format is described herein (in terms of the number ofinformation bits, etc.) using a particular network configuration. Thisdescription of such an exemplary implementation addresses the modulationof payload information. Other elements of transmitted waveforms caninclude: pilot, acknowledgement, and power setting communications. Forthe purposes of this explanation, bursts can be described as transmittedwaveforms communicating information.

In one embodiment, a burst can be formed as follows:

-   -   Input contains 112 payload information bits;    -   An appended 16-bit Cyclic Redundancy Code (CRC) yielding 128        uncoded bits;    -   Error correction coding, at rate 1/4, yielding 512 coded bits;    -   Each coded bit can be spread using a 256 bit Walsh code,        yielding a total burst length of 2¹⁷ bits;    -   A 1024 bit Gold code can be combined (in this case via an XOR        function) with groups of 4 coded bits (each spread by a 256        Walsh code), wherein each such group has the duration of a        timeslot. Each quarter of a timeslot, associated with a Walsh        code, is called a symbol. That is, each coded bit corresponds to        a symbol.

There can be 128 timeslots and 512 symbols in each burst;

-   -   Each of the 2¹⁷ bits in a burst can be transmitted as a chip        (i.e. a filtered waveform) with time spacing (from        chip-to-chip), of a chip period; and    -   The time taken to transmit 2¹⁷ chips is a frame.

The timing of bursts transmitted by terminals can be defined in terms ofreturn transmit slots, which are times within frames that are identifiedby return transmit slot indices. The times are selected to provide goodperformance in reception of the bursts. More specifically, the definedtimes reduce the probability of simultaneous reception of bursts fromdifferent terminals that are aligned in timeslots.

In one embodiment, an exemplary network configuration can include thefollowing parameters:

-   -   Forward Link Carrier Frequencies and numbering (Absolute Radio        Frequency Channel Number or “ARFCN”);    -   Chip Rate;    -   Filter characteristics, e.g. Roll-Off factor of Square-Root        Raised Cosine; and    -   Frame Reference to enable time definition.

Sample parameter values in one exemplary embodiment can be set asfollows:

-   -   Forward carrier frequencies at 1,525,000,000+31,250*N; where        1≤N≤1,087    -   Chip Rate=23,400 cps    -   Roll-Off Factor=0.35    -   Frame Reference based on GPS time, starting at a particular date        and time, e.g. UTC (midnight) of Jan. 1 to 2, 2017.

The 512 coded bits transmitted can each be associated with a 256-bitWalsh coded sequence. Each Walsh coded sequence can be selected from oneof 256 possibilities, each defined by a Walsh Code Index. Selection ofthe Walsh codes can give a degree of freedom in the design of a system.For example, the set of Walsh codes used for transmission of BCCHchannels can be a key to Forward Link synchronization. As mentionedabove, conventional satellite communications systems typically do nothave air interface capabilities of the type described herein withrespect to various embodiments of the invention, which are capable ofcommunicating a complete message without establishing a connectioninvolving several or many burst transmissions.

Scheduled transmissions can be a key capability in various embodimentsof the invention. The following description outlines various embodimentsof scheduled transmission establishment and execution.

During terminal registration, the central server could establishscheduled transmissions to be performed by that terminal. The followingset of parameters provides an example of the information that may passedto the terminal. In one embodiment, 54 bits of transmitted informationconsist of 3 parameters and the combination of these parameters can becalled an Information Element. For example, Information ElementTI_IE_Sched_TX_Config can comprise parametersTI_ELMT_Sched_TX_First_Frame, TI_ELMT_Sched_TX_Frame_Incr, andTI_ELMT_Sched_TX_Timeslot. TI_ELMT_Sched_TX_First_Frame can comprise 23bits, TI_ELMT_Sched_TX_Frame_Incr can comprise 23 bits, andTI_ELMT_Sched_TX_Timeslot can comprise 8 bits. The first element,TI_ELMT_Sched_TX_First_Frame, can define the 23 Least Significant Bits(LSBs) of the frame number of the first transmission (e.g., it can havea range of ˜543 days if the chip rate is 23.4 kcps). The second element,TI_ELMT_Sched_TX_Frame_Incr, can define the number of frames betweentransmissions (which can also have a range of ˜543 days if the chip rateis 23.4 kcps). The third element, TI_ELMT_Sched_TX_Timeslot, can defineon which of the timeslots within the selected frame the terminal shouldbegin transmission.

The assignments of frames and timeslots can be arranged to ensure thateach terminal has a unique transmission start time. For example, whenthe time of the first scheduled transmission is approaching (perhaps 100seconds beforehand), the terminal can acquire and then receive theforward link control channel, the BCCH. The terminal can then read someof the content of the System Information to determine whether it shouldproceed with the scheduled transmission. That is, the terminal can checkthat channel quietening is not active and that transmission is enabled.The terminal can also read other System Information related todetermining the terminal's initial burst transmit power. The terminalmay then execute a protocol that begins with transmission of thescheduled transmission burst 1202, as shown in FIG. 12. As thetransmission time approaches (perhaps a few seconds beforehand), theterminal can determine the appropriate initial burst transmit power,prepare the burst for transmission, and the associated real-time controlregisters can be programmed to enable the transmission to begin. Then,at the selected transmission time, the burst can be transmitted. Asshown in FIG. 12, the terminal will then receive a burst 1204 from thehub. If that burst contains an ACK indication, then the protocol willend, and the terminal will return to a dormant state and wait for thenext scheduled transmission. If a NACK indication is received, then theterminal will retransmit the burst at a pre-defined retransmission time.Retransmissions will continue until an allowed maximum number of retriesis reached.

FIG. 13 illustrates one embodiment of the subject invention in whichmultiple terminals, located in the same beam, execute scheduledtransmissions. Terminals located in beams other than the one illustratedhere may use different Gold sequences and thus are typically not seen byHub 1312. The four terminals 1304, 1306, 1308, 1310 can be assigneddifferent transmit times as illustrated in FIG. 15. TheTI_IE_Sched_TX_Config Information Element can be used to assign thedifferent scheduled transmission times for bursts 1502, 1504, 1506, and1508. As shown in FIG. 13, terminal 1304 can be a mobile terminalattached to a moving vehicle, terminal 1306 can be a mobile terminalattached to a house pet, terminal 1308 can be a mobile terminal attachedto a bicycle, and terminal 1310 can be a mobile terminal attached to aboat. The terminals 1304, 1306, 1308, 1310 can be configured to sendburst messages to the network infrastructure (satellite hub 1312 andcentral server 1314) through the satellite 1302 at differentpre-determined times such that the network infrastructure can match upthe burst messages with the sending terminal based on the time ofreception of the burst message at the network infrastructure. In thisway, message overhead can be reduced because terminal identityinformation as well as other overhead typically found in a conventionalcommunication system, is not needed.

FIG. 14 illustrates an exemplary scheduled transmission process for aterminal according to one embodiment of the invention. Each terminal ina system can implement scheduled transmissions as shown in FIG. 14.According to FIG. 14, the terminal first wakes up 1402, then acquiresthe pilot waveform 1404 resulting in resolution of timeslot boundaries.Burst framing can be determined by the terminal based on Walsh codesequences associated with the BCCH 1406. The terminal then reads theSystem Information 1408 and, based on the content of the SystemInformation, the terminal can determine whether to proceed 1410 with thescheduled transmission, or to reschedule for a later time 1412. Itshould be noted that a version number can be associated with the SystemInformation. In this manner, it is possible for the terminal to checkthe version number of the System Information and, if it matches theversion number of System Information previously read and stored by theterminal, the terminal can use the stored System Information instead ofusing bandwidth to re-read the System Information. If it is determinedthat the transmission should proceed, the terminal will calculate theinitial burst transmit power and wait for the assigned time 1414 andthen transmit the burst 1416 at the scheduled time using the calculatedinitial burst transmit power. After transmission, the terminal willreceive an acknowledgement (ACK or NACK) 1418. In the event an ACK isreceived, the scheduled transmission will be completed 1424 and theterminal will go back to sleep. If a NACK is received, the terminal willprepare to retransmit the burst 1422 (which includes raising the powerby a parameterized number of dB's as described more fully herein), andthen repeat the transmission and acknowledgement steps 1414, 1416, 1418,1420 until the burst is successfully transmitted.

The maximum number of retransmission attempts can be limited by aparameter that can be delivered via System Information. The hub receivercan be configured to receive transmitted bursts from each of the fourterminals. The spreading codes (Gold and Walsh) can be used to enablethe separate reception of each burst. These bursts may overlap in time.Low auto-correlation of the spreading sequences can enable reception ofbursts which overlap in time. The time at which the bursts are receiveddepends on the transmission time and the length of the signal paths. Themaximum difference in signal delay across a beam is usually less thanthe difference between the assigned transmission times. Signal delay canarise both in the forward link, from which the terminal derives its timereference, and the return link, through which the transmission passes.As a result, the arrival time of each burst can be unambiguously mappedto the source terminal.

MSS satellites, potentially in combination with ground-based facilities,can generate beams enabling communication in the forward(satellite-to-terminal) and return (terminal-to-satellite) directions.In typical forward link implementations, a phased array of emitters atthe satellite transmits power that is reflected by large antenna (with awidth of tens of meters). In the return link, a phased array of receiverelements forms similar beams. As shown in FIG. 4, in an exemplarysatellite communication system 400, a satellite 402 may providecommunication links to areas on the Earth's surface. Using a beamformer, the satellite 402 can direct signals 404 to areas on the ground,for example, creating beams 408, 410, 412. Typical satellites createhundreds of beams, where each beam is hundreds of kilometers indiameter. Within a beam, multiple carrier frequencies may provideconnectivity (in each direction 404, 406). Neighboring beams (such as408 and 410) can use the same carrier frequency. A satellite terminal414 within a beam 412 can be assigned resources associated with thatbeam 412. Multiple satellites may create beams that cover a satelliteterminal, which means that operational mapping between each satelliteterminal and a satellite (and beam) should be determined.

FIG. 17 shows a partial communication system 1700 with a satellite 1702in orbit above the Earth's surface 1704. The satellite 1702 communicateswith a terminal 1708 by creating a beam 1710 on the Earth's surface1704. When the terminal 1708 is located within the beam 1710 a signalpath 1706 between the orbiting satellite 1702 and ground-based terminal1708 can be created. Typical system designs are based on a paradigm ofcoincident forward and return link geographic beams, i.e., the beams(such as beam 1708) can be defined in terms of a polygon (typicallyusing latitude and longitude units) where that polygon is the same forthe uplink and downlink. That is, such a polygon is referred to as ageographic beam 1710. The radiated beams form a beam gain pattern 1712which is formed by the radio frequency elements overlaying thegeographic beams 1710 and will differ in shape between the forward andreturn link for many reasons including that they are generated bydifferent hardware at different frequencies. From the satellite's 1702perspective, the formed beams (such as beam 1708) have widths that aretypically in the order of 0.2 degrees.

As shown in FIG. 19, embodiments of a communication system 1900 caninclude a satellite 1902, a terminal 1904, and network infrastructureincluding a gateway and network 1906. The terminal 1904 communicateswith the gateway and network 1906 through the satellite 1902 on anreturn communication link 1906 and the gateway and network 1906communicate with the terminal 1904 through the satellite 1902 using aforward communication link 1910. Service links 1912 can be used for theterminal 1904 to satellite 1902 communication with the uplink 1916providing communications from the terminal 1904 to the satellite 1902.Feeder links 1914 can be used for satellite 1902 to gateway and network1906 communication.

MSS satellites often operate in inclined orbits. That is, the plane ofthe orbit (nominally above the equator) is offset from the equatorialplane by angles in the order of 5 degrees (where this inclination variesover the life of the satellite). The purpose of allowing such inclinedorbit operation is to reduce satellite fuel consumption for stationkeeping. To maintain the location of beams on the ground, thebeam-forming mechanism adjusts the shape of the beams throughout theperiod of a sidereal day, i.e., the period of a satellite's orbit. Thisis typically done using discrete changes to the coefficients driving thebeam formation at intervals of, perhaps, tens of minutes. At the timethe coefficients change, so does the shape of the beams. In addition,even when the coefficients are not changed, the beam shape (as seen onthe ground) changes due to the motion of the satellite.

The gains in the forward and return link beams (as seen by a terminal)both contribute to the accuracy that can be achieved when setting thepower at the terminal's transmitter. By communicating this gaininformation to the terminals, the accuracy of power setting can beimproved. As a contributor to the determination of a terminal's transmitpower setting, description of the gain pattern in both the forward andreturn link beams can be provided via System Information. For example,the System Information can include information that described at leastone beam's shape in terms of gain as a function of spatial locationformed by the satellite's transmitter, gain as a function of spatiallocation formed by the satellite's receiver, gain differences betweenthe satellite's transmitter and receiver as a function of spatiallocation, or any number of other ways. These descriptions can enable aterminal to determine gain approximations related to the paths to andfrom the satellite as a function of the terminal's location.

Terminals will typically determine their locations using GNSS (GlobalNavigation Satellite System) receivers, e.g., GPS (Global PositioningSystem). Alternatively, for fixed-position terminals (e.g., in a utilitymeter), the position could be entered during configuration. If aterminal cannot obtain a location estimate by either of these means, theterminal could estimate its position using the observed SNR valuesassociated with the camped beam and its neighbors. A camped beam is abeam from which a terminal is receiving System Information. The terminalmay obtain these SNR estimates from correlations that arise duringacquisition. The position estimate could then be derived by the terminalby matching the observed SNR values with the beam pattern descriptions.In the case when the same carrier frequency is used for the forward linkpilot in neighboring beams, a terminal can estimate the SNR from severalbeams simultaneously. Once a terminal has established connectivity withthe network, it may provide the SNR estimates to the network, whichcould generate a similar position estimate. The network could have theadditional advantage of observations of the received signals from theterminal in multiple beams, the Round-Trip Time, and potentially moredetailed beam pattern estimates.

In various embodiments of the invention, communication links usesporadic transmission of a small number of bursts, frequently a singleburst. Sporadic can mean, for example, daily or monthly individual bursttransmissions. This environment differs from situations in which manybursts are transmitted with short inter-burst intervals (where short isrelative to the rate at which the channel conditions change). Shortinter-burst transmissions, for example, could occur at regular intervals(e.g., every 20 ms), or could be less regular. For example, they couldbe dependent on packet user traffic and possibly with keep-alive bursts(i.e., special transmissions aimed at maintaining synchronization andpower setting in a link). Power control in such continuous ornear-continuous transmission situations is typically based on open-loopinitialization, followed by closed-loop tracking and correction. As themajority of bursts are transmitted with closed loop control, theprecision of open loop corrections has low impact on overall powercontrol effectiveness.

In the case of sporadic transmissions, such as the single burst messagessent in embodiments of the invention, power is primarily set based onopen-loop corrections. As such, the precision of open-loop estimates ofsuitable power levels gains significance in terms of overall powerefficiency and capacity. To determine the level of the transmit power, aterminal can consider some or all of the following information:

-   -   The received pilot Signal-to-Noise Ratio (which can be estimated        during the demodulation process at the terminal receiver);    -   An estimate of the gain difference between the forward and        return link gain patterns at the terminal's location (which can        be read from the broadcast System Information);    -   A long-term updated correction, based on feedback from the        network regarding prior transmission (which can be stored at the        terminal based on previous communications);    -   A constant corresponding to the link budget (which can be read        from the System Information); and    -   A power offset corresponding to current interference conditions        (which can come from the satellite when the terminal listens to        the forward link prior to sending its burst message).

A communication system could support several modes of connectivityincluding scheduled transmission, broadcast, alarm transmissions, and/orpage transmissions, to mention a few. Some applications might benefitfrom timely delivery of information. For example, the triggering of anintrusion alarm or high-temperature alarm might be reported promptly.“Rapid Alarms” and “Rapid Pages” are described below, where theseconnectivity options support communication in the return and forwarddirections, respectively.

In the case of a Rapid Alarm, a burst containing time-criticalinformation can be transmitted from a terminal to the network. Two keyaspects of the burst can be (1) it has enough payload to convey theassociated information, and (2) the burst can be transmitted at a highrate. In order to select a high transmission rate, the terminal shouldconfirm that the return link channel has enough margin to enable a highprobability of successful communication at that rate. To do this, theterminal combines the power control information derived above withknowledge of the additional power associated with higher transmissionrates. The terminal may have multiple options regarding the transmissionrate, based on network-advertised (e.g., via System Information)possibilities.

Satellite communications channels may be shared. Generally, acommunications channel is a frequency band, with a lower and upperfrequency, through which a waveform can be transmitted. A communicationchannel could be shared, for example, by a forward link transmissionaccording to the subject application and the BCCH of another airinterface. When channels are shared, the operation of the links can beimpacted. For example, the Signal-to-Noise Ratio measured at theterminal receiver may be lower than it would have been in a dedicatedchannel, i.e., where the communications channel is not shared. Thisdifference could impact the power control, where open-loop actionsdepend on the received signal metrics. By informing the terminals of thenature of the sharing of a communications channel, performance can beimproved. If a terminal is aware of the characteristics of theco-channel interference (the shared signal), then it may adjust thepower control mechanism. For example, knowing that the shared channel isactive, and that it uses bursts of length 20 ms, the terminal couldobserve the received signal over several seconds, and excise the periodswhen the interference is active from the calculation of Signal-to-NoiseRatio.

In the process of determining the appropriate transmit power, a terminalis implicitly determining an estimate of the margin in that power. Forexample, if a terminal determines that it should transmit at −0.2 dBm,and the terminal's peak power capability is 10 dBm, then the margin is10.2 dB. From this number, the terminal can determine whether or not itcould transmit at a higher data rate, e.g., if an alternative bearerrequires 6 dB more power than the current bearer, then the terminalcould conclude that the alternate bearer is a viable option, and thatthe associated power should be 5.8 dBm.

If the terminal's position estimate has uncertainty corresponding toseveral kilometers, then the terminal may determine that it cannot beconfident of the accuracy of its transmit timing. Such errors lead tothe possibility of coincident pilot sequence reception (which candegrade reception performance). To mitigate this possibility, theterminal can apply frequency offsets to increase the probability ofsuccessful reception of the related burst.

Terminal transmit timing can be defined via instructions from thenetwork. That is, burst transmit times can be deterministicallypreassigned without conflict. For other connection options (e.g., aRandom Access burst), the terminal may autonomously select atransmission time. To reduce the probability of timing conflict (betweenpreassigned and non-preassigned transmissions), these non-preassignedbursts can be allocated separate transit time opportunities. Inaddition, frequency offsets can be applied to enable reception ofsimultaneously transmitted bursts to address the possibility that twonon-preassigned bursts happen to coincide in time.

If significant timing errors are present in transmitted bursts, it ispossible that the network receiver will not be certain of the timeslotwithin which the burst was transmitted. This information may impact thedetermination of the identity of the transmitter, leading to ambiguitythat should be resolved. Information embedded in the transmitted burstas a distinct code pattern enables resolution of this ambiguity. Asbriefly mentioned above, prior to transmission, terminals can read theSystem Information describing the forward and return link beam shapes,and can use this information to determine the optimal transmit power.Many approaches can be used in defining the shape of beams. Thefollowing is an example. It is desirable to target accurate gainestimates with a modest quantity of parametric information. The gainpattern (beam shape) of both the forward and return beams can becommunicated to terminals via the System Information (SI). Thedescription of uplink and downlink beams may consist of parameters suchas those listed below:

-   -   SI_(FWD and RET)_beam_width_control: a parameter defining the        spread of the beam pattern in the East-West cross section,        corresponding to the beam width;    -   SI_(FWD and RET)_beam_EW_NS_ratio: a parameter allowing control        over the difference in width of the beam in the North-South        cross section vs. East-West;    -   SI_(FWD and RET)_beam_center_offset: a vector corresponding to        the offset between the geographic beam center to the radiated        beam center;    -   SI_(FWD and RET)_beam_center_frame_number: the frame number at        which these parameters are defined (as the terminal is aware of        the satellite's motion profile);    -   SI_FW_beam_EIRP: the EIRP of the pilot in the BCCH containing        the SI;    -   SI_FWD_neighbor_beam_EIRP: the EIRP of the pilot in the BCCH of        each neighboring beam; and    -   SI_RET_beam_G_over_T: the G/T of the return beam.

In various embodiments of the invention, beam gain information isdefined from the satellite's perspective, i.e., at angular offsets froma beam center. The beam center itself typically lies at a 2-D angularoffset from the boresight of the satellite's antenna. The cross-sectionof narrow formed beams (i.e., where the antenna and the array ofemitters or receivers are forming the narrowest practical beams) isusually consistent for the range of gain of interest (˜3 dB within thegeographic beams). Therefore, that consistent pattern can be used as abasis for compression of the beam definition information.

Beam shapes can typically be approximated by equation including thosebased on sin(x)/x or Bessel functions. For purposes of illustration,embodiments of the invention are described herein using the sin(x)/x (orsinc) functions. However, it should be understood that other beam shapedescription techniques can also be used.

The cross-section of a beam pattern is likely to be radially similar,i.e., close to the same when cut across any angle. In order toaccommodate some variation, different spreads as a function of angle aresupported in the East-West vs. North-South cross sections (withelliptical variation assumed at other angles). In alternativeimplementations, the frames-of-reference can differ, e.g., along a linepassing through the satellite's boresight and the beam's geographiccenter, and at 90 degrees from that line.

Beam profiles can be generated using the formula Gain_dB(p,theta_deg)=sin((e^(p))*theta_deg)/theta_deg. In this equation,theta_deg represents angles seen from the satellite's perspective, the“p” parameter controls the width of the beam, and e corresponds to theconstant e (Euler's number). In various embodiments of the invention,the parameter SI_(FWD and RET)_beam_width_control can be used for “p”.The theta_deg variable, which is the angular offset of the terminal asseen from the satellite's perspective relative to the center of the beamcontaining the terminal can be determined by the terminal.

The exponential (e^(p)) is applied so that sensitivity to the parametervalue “p” has a low variation across the applicable range. The parameter“p” comfortably covers the range of possible beam widths (0.04 degreesto 1.1 degrees) using the range 1:4 and, for some of the embodimentsdescribed herein, the maximum step size in power per parameter unit “p”is 1.1 dB. A step-size in the parameter (p) of 1/128 can ensure thatsteps in power are less than 0.1 dB over the required range. That is, astep size of 1.128 over a range from 1 to 4 is sufficient, i.e., 9 bits.A conservative implementation (i.e., one with 2 additional bits) of therelated parameter, p (which can be SI_FWD_beam_width_control orSI_RET_beam_width_control), could be formatted as an 11 bit unsignedvalue. In the 11 bit scenario, p=p_min+N*(1/256). Thus, p=p_min(which=0) when the N is 0 and the maximum value (when N=2047) is2047/256 (which=7.996).

The position of the beam center can be defined by SI_beam_center_offset.The location of the center of the radiated beam can have some errorrelative to the geographic center. This offset can be passed to theterminal via the System Information. At the edge of coverage forrepresentative small beams (0.15 degrees width), 0.1 dB change in poweroccurs with a ˜0.001 degrees change in beam location. Assuming a maximumerror of 0.25 beam widths and a 0.5 degree beam, the range of theparameter would be −0.125 to 0.125, implying that an 8-bit parameter ineach direction would be sufficient. A conservative implementation (i.e.,one with 2 additional bits) of the related parameter, c (which can beSI_beam_center_offset), could be formatted as a 10 bit signed value. Inthe case of a 10 bit signed value, c=c_min+N*(0.0005). Thus, c=c_min(which=−1.024) when N is 2048 and the maximum value (when N is 4095) is1.0235 (−1.024+4095 (0.0005)).

The ratio of the cross sections of the beam could be defined bySI_beam_EW_NS_ratio. The expected value of this ratio is 1 and the rangeof variation is probably less than +/−10%. Given the sensitivity toerror, where ˜0.6% (0.001 out of 0.150 degrees), a reasonable step sizecould be 0.3% over a range of +/−20%, requiring 7 bits. A conservativeimplementation (i.e., one with 2 additional bits) of the relatedparameter, r (which can be SI_beam_EW_NS_ratio), could be formatted (inpercentage units) as a 9 bit signed value. In the case of a 9 bit signedvalue, r=r_min+N*(1/6). Thus, r=r_min (which=−42.66%) when N is −256 andthe maximum value (when N is 511) is 42.5% (−42.66+511/6).

The EIRP can be defined by SI_beam_EIRP. The EIRP of the pilot of theBCCH will typically be ˜33 dBW in the direction of maximum gain, i.e.,the peak of the beam pattern. The beam EIRP is typically defined at theedge of the beam, where it can be −2-3 dB lower. The range of valuesaround this level could reasonably be +/−10 dB. Hence, a reasonablenumber of possible values could be ˜200, corresponding to 8 bits. Aconservative implementation (i.e., one with 2 additional bits) of therelated parameter, e (which can be SI_beam_EIRP), could be formatted (indBW) as a 10 bit unsigned value. In the case of an unsigned 10 bitvalue, e=e_min+N*(0.05). Thus, e=e_min (which=0) when N is 0 and themaximum value (when N is 1023) is 51.15 dBW (0.0+1023*(0.05)).

The G/T can be defined by SI_beam_G_over_T. The G/T of the receiver willtypically be ˜10 to 24 dB/K in the direction of maximum gain. The rangeof values around this level could reasonably be +/−10 dB. Hence, areasonable number of possible values could be ˜400, corresponding to 9bits. A conservative implementation (i.e., one with 2 additional bits)of the related parameter, g (which can be SI_beam_G_over_T), could beformatted (in dB/K) as a 10 bit unsigned value. In the case of anunsigned 10 bit value, g=g_min+N*(0.05). Thus, g=g_min (which=0) when Nis 0 and the maximum value (when N is 1023) is 51.15 dB/K(0.0+1023*(0.05)).

The forward link beam patterns provided to the terminals via SystemInformation can be used as a basis for approximation of the terminal'slocation. While neighboring beams may or may not use the same carrierfrequencies, the example described herein is based on use of the samefrequencies. If neighboring beams use different frequencies, a similarapproach could be applied (although possibly with diminished accuracy).In other words, in various embodiments described herein, a terminal canreceive and perform a correlation with a waveform.

In each beam, a forward link transmission can include a pilot waveformwhere the same chip sequence is used in each beam, but the sequence isoffset in time for each beam. As such, no two neighboring beams will usethe same time offset. The EIRP transmitted from the satellite may varyfor neighboring beams. One advantage to such differences is that asimilar link margin is provided in neighboring beams even when thosebeams may have differing path lengths to the satellite. When receivingthe pilot waveforms from the occupied beam and its neighbors, theterminal can correlate the sequences with the hypothesized pilotsequence and observe levels of correlation that are proportional to thepilot levels being received from each beam. The signal levels from eachbeam's pilot can be received simultaneously and can all be impacted bythe same thermal noise. As a result, the pilot levels can provide auseful indication of the relative levels of each pilot signal astransmitted by the satellite and after being attenuated by the beamformer.

The relative pilot levels observed can then be matched with the forwardlink gain of each of the beam formers. The terminal should be aware (viathe System Information in the camped beam) of the relative time offsetsof each of the beam's neighbors. Using the know EIRP differences betweenbeams, the terminal can determine power adjusted correlation values. Theterminal can select the three highest level power adjusted correlationestimates (from among up to 7 beams) that correspond to three beams thatshare a vertex. The terminal can determine differences in correlation(in dB units) between the three levels. The terminal can use the forwardlink beam definition as a model for each of these three beams.

The terminal can find the location best matching the differences incorrelations. The difference in correlation between the highest andsecond highest correlations can correspond to a line on the earth'ssurface. The difference between the highest and third highestcorrelations can correspond to another line on the earth's surface. Thepoint at which the lines intersect corresponds to a position estimatefor the terminal.

A more precise position estimate could be generated at the network,based on the same correlation measurements, possibly in combination withRound-Trip Times. That is, the terminal could report the observedcorrelations to the network, which could match those correlations withmore accurate models of the formed beams. The network could observetransmissions from the terminal via the receivers in several beams,enabling a similar position estimate based on SNR values at thesatellite.

Return link power control can utilize the beam gain information forpower control calculations. In generating the terminal transmit powerlevels, a variety of different information is combined. For example, theperceived SNR of the forward link pilot (SNR_pilot_dB), which providesan indication of the loss in the forward link, can be used. Aparameterized power increment provided by the network (Power_incr_dB)can also be used. This is a value that enables the network to controlthe power of all terminals in a beam. The level can be raised when thebeam approaches capacity, i.e., the interference power approaches thenoise power. A long-term estimate in the terminal correcting forperceived differences in the forward and return link gains of theantenna (TD_FWD_RET_gain_diff_est_dB) can also be used. This estimatecan be based on the history of correction information passed to theterminal after previous (sporadic) transmission. The terminal may usethe direction of the satellite (Azimuth and Elevation) to refine itsinternal antenna model in terms of relative receive and transmit gain. Aparameterized value representing the gain difference between the Forwardand Return link gains at the satellite provided by the network(Sat_FWD_RET_gain_diff_est_dB) can be used in the power controlcalculation. This value may be passed to the terminal using a set ofparameters that characterize the variation of gain across the beam andover time. Finally, a parameterized constant providing an offsetassociated with the link budget (Link_constant_dBm) can be used in thepower control calculation.

In one embodiment, the above-mentioned information can be used todetermine the open-loop transmit power using the equation:

Transmitpower=Power_incr_dB+TD_FWD_RET_gain_diff_est_dB+Sat_FWD_RET_gain_diff_est_dB−SNR_Pilot_dB+Link_constant_dBm

A typical Transmit power value can be about −0.2 dBm based on typicalvalues for the factors being: Power_incr_dB˜2 dB;TD_FWD_RET_gain_diff_est_dB˜−1.3 dB; Sat_FWD_RET_gain_diff_est_dB˜0.7dB; SNR_pilot_dB˜−18.0 db, in units of Ec/No; andLink_constant_dBm˜−19.6 dBm.

The energy required to transmit a fixed quantity of data does not depend(significantly) on the power level, i.e., data can be transmitted overlonger periods with less power or shorter periods with more power. Thenature of each application can drive the need for timeliness ofdelivery. Applications such as daily utility meter reading may havemodest latency requirements, perhaps many minutes. Other applications,such as reporting of a facility intrusion, might be better served byquicker message delivery, perhaps within a second. Given fixed maximumpower capability in a terminal, achievable latency can depend on thelink margin at the time of the transmission. Link margin can be definedas the difference between the required power and the available power.The accuracy with which that margin can be estimated can drive theability of a terminal to achieve low latency when needed.

Bursts can be transmitted by terminals at different information bitrates. In some connectivity modes, the terminal can autonomously selectthe time to transmit and the information rate to apply. This mode ofoperation is particularly useful in cases where the delay in delivery ofinformation from terminals to the network is important. One approachtaken in various embodiments described herein is to support twodifferent data rates called “baseline” and “eight times baseline.”

When operating at a “baseline” information data rate, the input cancontain 112 payload information bits. Adding an appended 16-bit CyclicRedundancy Code (CRC) yields 128 uncoded bits. Error correction coding,at a rate of 1/4, yields 512 coded bits. Each coded bit can be spreadusing a 256 bit Walsh code, yielding a total burst length of 2¹⁷ bits. A1024 bit Gold code can be combined (in this case via an XOR functions)with groups of 4 coded bits (each spread by 256 Walsh codes), such thateach group has the duration of a timeslot. Each quarter of a timeslot,associated with a Walsh code, is usually called a symbol. That is, eachcoded bit corresponds to a symbol. In this case, there can be 128timeslots and 512 symbols in each burst. The same 1024 bit Gold code canbe used to generate a pilot waveform, in combination with a 256 bitWalsh code, where the Walsh code is orthogonal to the Walsh codes usedfor the coded bits. Each of the 2¹⁷ bit combinations (pilot and traffic)in a burst can be transmitted as a chip (i.e., a filtered waveform) withtime spacing (from chip-to-chip), of a chip period and the time taken totransmit 2¹⁷ chips is a frame.

When operating at an information data rate that is “eight timesbaseline,” a similar approach can be taken with some key differenceswhich are highlighted as italicized text. In this case, the input cancontain 112 payload information bits. Adding an appended 16-bit CyclicRedundancy Code (CRC) yields 128 uncoded bits. Error correction coding,at a rate of 1/4, yields 512 coded bits. Each coded bit can be spreadusing a 32 bit Walsh code, yielding a total burst length of 2¹⁴ bits. A1024 bit Gold code can be combined (in this case via an XOR function)with groups of 32 coded bits (each spread by a 32 bit Walsh code), suchthat each group has the duration of a timeslot. There can be 16timeslots in each burst. The same 1024 bit Gold code can be used togenerate a pilot waveform, in combination with a 256 bit Walsh code,where the Walsh code is orthogonal to the Walsh codes used for the codedbits. The 256 bit Walsh code used differs from the code used at thebaseline data rate. Each of the 2¹⁴ bit combinations in a burst can betransmitted as a chip (i.e., a filtered waveform) with time spacing(from chip-to-chip), of a chip period and the time taken to transmit 2¹⁴chips is an eighth of a frame.

In summary, a terminal could transmit at two (or more) different datarates. For a terminal transmitting at a higher rate, the thresholdSignal-to-Noise Ratio would generally also be higher. As the terminalcan autonomously select the information data rate, it could determinewhether the achievable Signal-to-Noise ratio is sufficient to supportthe selected rate. This information can be implicitly derived during theprocess of determining the appropriate power for transmission asdescribed for power control.

For example, when considering a terminal operating at the baseline rate,the terminal combines the measurements and parameter values, anddetermines that the transmit power (dBm) is −0.2 dBm. If the terminalhas a maximum transmit power capability of 10 dBm, to transmit at 8times the base line rate, the terminal could determine that it wouldneed 9 dB of additional power. Note that this could be derived from thedata rate difference directly (10*log 10(8)) assuming no change inenergy per information bit, or there could be differences in Ebi/Noperformance that can be taken into account. That is, the terminal candetermine that to transmit using the higher rate bearer, it would needto transmit at −0.2+9=8.8 dBm. As this is below 10 dBm, the terminalwould have this option.

The design of spreading sequences used for terminal transmission caninvolve several tradeoffs. For example, the pilot waveform might bebased on a pseudo-random sequence that continues for the length of aburst or it might use a shorter sequence that is repeated several timesduring the burst. The approach of using shorter, repeated sequences issometimes referred to as a “repeated sequence pilot waveform.” Adisadvantage of using repeated sequences is that two transmissions fromdifferent terminals may have different start times of transmission, butcoinciding timing of the pilot sequences (and this can occur forsignificant portions of the bursts). This possibility is calledcoincident pilot sequence reception.

Terminal transmissions usually contain pilot waveforms that consist of128 repetitions of a 1024 bit pilot sequence. It is possible that twoterminals could transmit bursts that are received at the satellite withthe 1024 bit pilot sequences coinciding in time resulting in coincidentpilot sequence reception. This could lead to degraded performance in thenetwork receiver as the two signals from different terminals might notbe distinguishable by the channel estimation process.

When bursts are transmitted from more than one terminal, the network canusually reliably distinguish those bursts and demodulate their contents.In order for the bursts to be distinguishable, the pilot waveformswithin the burst should be separated in time by more than a chip period,i.e., coincident pilot sequence reception is avoided or the perceivedcarrier frequencies of the burst are separated by a frequency offset.The frequency separation needed depends on the implementation of thereceiver but typically values of ˜3 Hz or more usually work.

Return link bursts can be received at any time, i.e., the detection andreception processes operate continuously. However, to enable adistinction between transmitters and to avoid coincident plot sequencereception, transmission times can be assigned and applied by terminals.Over the period of a frame, 508 transmit opportunities can be definedand, in typical operation (as set by a System Information parameter),254 of these can be available. At a transmission rate of 23.4 kcps,there is one transmit opportunity every ˜22 ms. When viewed from theperspective of the pilot waveform, the targeted minimum time spacing oftransmit opportunities is 4 chips.

Actual transmission time can be impacted by error in the terminal'sestimate of its position. The acceptable error in a position estimatecan depend on the associated timing errors. Regarding the timing ofterminal transmissions, given a separation of 4 chips between assignedtransmission times, the combined error in timing between two terminalsshould be less than 3 chips periods, so the waveforms do not come within1 chip period time separation. Each terminal, therefore, should have aposition-related timing error of less than 1.5 chip periods. At 23.4kcps, this corresponds to a timing error of ˜64 us. Errors in timingtypically correspond to twice the distance error (as the referencesignal from the satellite experiences a first delay and the returntransmission to the satellite experiences a second delay). Assuming thatthe distance error is in the direction of the satellite (a conservativeassumption), the threshold position error would be˜3×10⁸×64×10⁻⁶/2=9,6000 m. Allowing comfortable margin for uncertaintyin the position estimation error, a reasonable threshold when definingthe acceptable error could be 5 km. If the terminal can reliablydetermine that its position error is within this range, then it can bedefined to have an accurate position estimate.

Errors in the order of kilometers in position estimates can arise in avariety of ways. For example, if a terminal has a GPS location andsubsequently moves (and does not get a fresh fix), then the worst caseposition error can be estimated based on the maximum speed of theterminal and the time since the fix was obtained. Another example is ifa terminal's position estimate is based on SNR measurements from thepilot waveforms. In this case, the error could be well over 5 km.

Various circumstances can result in coincident pilot sequence receptionat the network receiver. For example, position estimation error at theterminals and simultaneous transmission of non-preassigned bursts (e.g.,due to coincident alarm events at the terminal inputs) can both resultin coincident pilot sequence reception.

Bursts transmitted by terminals can be categorized as either preassignedor non-preassigned. If both the terminal and the network are aware ofthe intended transmission of a burst and its transmit time, then thatburst can be considered preassigned. Otherwise the burst is typicallyconsidered non-preassigned. Terminals, being aware of these conditions,can apply frequency offsets to their transmitted bursts in both cases.The level of frequency offset can be defined by System Information(e.g., setting the units of separation to 3 Hz.) That is, the frequencyoffset could be set as 3N Hz (where N is a signed integer within adefined range). For transmissions with preassigned timing, the value ofN can be derived from the assigned Return Link Timeslot number. Forexample, the value could lie in the range 0:507 interpreted as a 2'scomplement value. For transmissions with non-preassigned timing (e.g.,RACH), the value of N can be derived from the CRC of the transmittedburst. The intent of this approach can be to ensure that simultaneouslytransmitted bursts (with the same Return Link Timeslot number) arelikely to use different frequency offsets.

The network can have awareness of the number of terminal transmissionsthat are preassigned and non-preassigned. In order to provide anadditional means of distinguishing the burst categories, the network mayassign specific transmit opportunities for each category. For example,preassigned bursts could be assigned to all even number Return LinkTimeslot numbers and non-preassigned bursts to odd numbers. Thisdistribution could be modified via System Information options.

Return link bursts can also be distinguished from one another byapplying different pilot pseudo-random sequences. These sequences couldbe applied by using the same Gold codes (as all other forward linktransmissions) and using different Walsh codes. One advantage of thisoption is to reduce the probability of coincident transmissions. Onedisadvantage is that it increases the complexity of the network receiverby requiring adding another pilot sequence hypothesis. To support thisoption, System Information could inform the terminals of the availableWalsh codes for Pilot generation.

One feature of embodiments of the invention is the ability to identifyterminals based on the time-of-arrival at the network of bursts sent bythe terminals. Terminals can use estimates of the distance to thesatellite from their location to correct the transmit timing such thatbursts arrive at the time corresponding to a particular location such asthe time center of a beam (half way between the closest and farthestpoints in a beam from the satellite). Terminals with degraded locationestimates may transmit with timing errors. In beyond-worst-caseconditions, this timing error could reach a range in the order of +/−28ms.

The beams at the edge of coverage (where terminals see the satellite atthe lowest elevation) can have higher variation in the distance to thesatellite relative to beams that are closer to the sub-satellite point.The worst-case beams can have edges with zero degree elevation towardsthe satellite. Note that systems typically aim to provide service athigher elevations (e.g., 20 degrees and above). However, it could beuseful to enable operation at lower elevations. The width of beams isnear fixed as seen from the satellite. Maximum diameters of existingspot beams can be approximately 1.25 degrees. A terminal can typicallydetermine its location (based on GPS or SNR measurements) within 0.25beam widths. A beyond-worst-case assumption, therefore, could be that aterminal could have a position estimate that is 50% of the beam'sdiameter beyond a beam's edge when its actual location is 50% of thebeam's diameter on the opposite beam's edge. This could result in aone-way delay range of around 14 ms. As terminal's base their transmittimes on the received time of network-originated signals, the range ofreception time at the satellite (and network) could be approximately 28ms, assuming a fixed receive-to-transmit time offset at the terminal.With the terminal adjusting its transmit time (to target correct timing)the delay could range over +/−28 ms (a 56 ms range).

At nominal rates (23.4 kcps), the minimum separation betweentransmission opportunities could be ˜11 ms. To ensure that bursts can bereceived without ambiguity in a receive timing window, a means fordistinguishing each of every 8 bursts could be needed. This wouldsupport an error range of up to ˜88 ms, where the requirement is ˜56 ms.The mechanism for distinguishing the bursts could take any of severalforms. This set of options can be referred to as a set ofdistinguishable code patterns. A low-complexity, robust example of acode pattern can be to apply masks to the CRC included in each burst.That is, the 3 least significant bits of the timeslot index can bemapped to a mask for the CRC. It may also be possible that other statusinformation could use the mask, such as a single bit to distinguishprearranged bursts from non-prearranged bursts.

By way of example, the CRC mask could be generated as follows: the 3bits associated with the timeslot index can be appended to a 4^(th) bitindicating the presence of a non-preassigned burst. These 4 bits couldbe placed in the least significant 4 bits of an 8-bit value, with theother bits set to zero. The 8-bit result could be repeated to generate a16 bit mask to be applied to the CRC (via eXclusive OR, XORcombination).

When receivers determine SNR estimates, account can be taken of thenature of any sharing the communication channel might imply. Threeparameters could be passed from the network to the terminal. Theyare: 1) a flag to indicate whether the channels are shared; 2) anindication of the minimum duration of the interfering signals (e.g., 5ms); and 3) an indication of the EIRP of the interfering signal (e.g.,40 dBW). These parameters could be passed to the terminal through thebroadcast System Information or through individual control messaging.

A terminal could use this information to assist in excision of theinterference from a received signal. For example, assuming a 5 secondobservation, 20 ms burst length, and a 40% duty cycle in the interferer,the terminal would typically see 3 seconds of received waveform in whichthe interferer is not present. It could use the minimum duration as abasis for excision. The EIRP could be used to further enhance the powercontrol as the received level could be used to independently estimatethe attenuation in the link.

FIG. 18 illustrates the various information that can be used whendetermining terminal characteristics. For example, the GNSS-basedposition estimation 1802, SNR Estimates 1806, and Beam patterns 1808 canall be used when determining a position estimate 1804. The Positionestimate 1804, as well as SNR Estimates 1806, and Beam patterns 1808 canbe used to determine data rate selection 1814. The Position estimate1804, SNR Estimates 1806, and Beam patterns 1808 can also be used todetermine the terminal initial power level setting 1816. The GNSS-basedposition estimation 1802 and Time and Frequency estimates 1810 can beused to set the frequency 1818. The position estimate 1804, Time andFrequency estimates 1810, and Satellite-Terminal relative positioncalculation 1812, can be used to set the timing 1820.

In some instances, particularly when the number of satellite terminalswithin a beam is large, it may be advantageous to provide a terrestrialreceiver for the satellite terminal transmissions. FIG. 5 illustrates anembodiment of a satellite communication system 500 in which a satelliteterminal 506 receives downlink signals 504 from a satellite 502 buttransmits 508 to a terrestrial hub 510. This architecture can beparticularly advantageous to applications, such as utility metering, inwhich most of the communications traffic is in the direction fromsatellite terminals 506 to a central server 512. In this embodiment,information from satellite terminals, such as 506, within wirelesscommunications range of the terrestrial hub 510 could be received by theterrestrial hub 510. Terrestrial reception could use the same terminaltransmit channel as that used for the satellite link. The terrestrialhub 510 could be configured to be aware of the delay to the satellite502, and thus could determine the expected time and frequency ofreceived bursts. As such, the satellite terminal 506 need not be awareof terrestrial reception.

The terrestrial hub 510 can be configured to change the satelliteterminal 506 transmit power to match the needs of terrestrial reception.In many cases, this can result in significant power reduction. The powerchange can be implemented in a number of different ways. For example,the power change can be a gradual adjustment after each transmission orthe power can be adjusted via a paged exchange where the terrestrial hub510 individually instructs (via the central server 512, the satellitehub 514, and the satellite 502) each satellite terminal 506 to make achange in power. The range of power control of the satellite terminal506 to support satellite operation can be typically approximately 15 dB.For terrestrial operation, the required range can increase toapproximately 80 dB due to the variation in path loss in a terrestrialenvironment. The dynamic range can be reduced in a number of ways suchas using higher data rates when transmitting close to the terrestrialhub 510 or using multi-user detection at the terrestrial hub 510 toreduce the sensitivity to the difference in received power levelsbetween terminals 506.

In another embodiment, communications in both directions may be providedterrestrially, such as when the volume of traffic in both the uplink anddownlink directions becomes large. As shown in FIG. 6, the terrestrialhub 610 and satellite terminal 606 can be configured to communicate inboth the uplink 608 and downlink 604 directions terrestrially. Theterrestrial hub 610 and satellite terminal 606 can be configured to useadditional channels. As conventional satellite systems may use TimeDivision Multiple Access (TDMA) within each beam (and frequency reuseover several beams), the number of channels available for terrestrialCode Division Multiple Access operation with a beam could be a sizableportion of the satellite system's 600 available spectrum.

In general, a satellite must have line-of-sight access to a satelliteterminal in order to communicate with the satellite terminal. As shownin FIG. 7, a satellite terminal 704 may be shadowed from a satellite 702if the line of sight between them is obscured, such as by a tree 706 orother obstruction. Embodiments of the invention can include terrestrialrelays 708 which are ground-based transceivers that provide links 710,712 to a shadowed satellite terminal 704.

A terrestrial relay 708 can be configured to receive forward link 714communications in one or more channels from a satellite 702. Theterrestrial relay 708 can then retransmit the content to the shadowedsatellite terminal 704. Retransmission can occur at another frequencywithin the allocated forward link band, but typically not used directlyfrom the satellite 702 within the beam containing the terrestrial relay708. For example, the terrestrial relay 708 may receive forward link 714communications from the satellite 702 at a carrier frequency of Fdn andthen retransmit 710 the information to the shadowed satellite terminal704 at a carrier frequency of Fdn+ΔFdn.

Similarly, the terrestrial relay 708 can also be configured to transmitreturn link communications 716 to the satellite 702. The terrestrialrelay 708 can receive return link signals 712 from the shadowedsatellite terminal 704, frequency shift the received signals, andretransmit the frequency shifted 716 to the satellite 702. For example,the return link carrier frequency may be transmitted at a carrierfrequency of Fup+ΔFup from the shadowed satellite terminal 704 and theterrestrial relay 708 may convert the carrier signal to Fup forretransmission to the satellite 702.

The frequency offsets (ΔFdn, ΔFup) applied to both the forward link 714and return link 716 can be advertised in the broadcast systeminformation. In addition, the signals passing through the terrestrialrelay 708 in both the forward link 714 and return link 716 can also havea fixed delay. For example, the delay may be set at 0.1 ms (with atolerance of 5 μs). The shadowed satellite terminal 704 can be aware ofthe delay in the terrestrial relay 708 (as this is either a systemconstant, or a period defined in the broadcast system information) andcan also be aware that they are using a terrestrial relay 708 (as thefrequency of the forward link 710 coincides with a relay assignment).The shadowed satellite terminal 704 can adjust its transmit timing suchthat its transmissions arrive at the satellite 702 at an intended time(i.e., the central server 720 and satellite hub 718 need not be awarethat the shadowed satellite terminal 704 is operating via a terrestrialrelay 708). Alternatively, status messages from the shadowed satelliteterminal 704 may inform the central server 720 whether or not it isoperating via a terrestrial relay 708.

The terrestrial relay 708 does not need to modify the content of datapassing through it. The terrestrial relay's 708 primary function can becarrier frequency conversion. In addition, the shadowed satelliteterminal 704 may be configured with sufficient margin in its schedulingof events to reduce the delay between reception and transmission ofsignals. For example, with a fixed delay of 0.1 ms in each direction inthe terrestrial relay 708, the change in delay at the shadowed satelliteterminal 704 could be 0.2 ms.

As described above, in various embodiments of the subject application,satellite terminals can communicate with network infrastructure usingscheduled burst transmissions that are intended to communicate acomplete message without all the overhead used in establishing andterminating a connection associated with conventional satellitecommunication systems. FIG. 8 illustrates one exemplary scheduledtransmission communication 800. During scheduled transmissions, asatellite terminal transmits a burst 802, where the content of the burstcomprises a pilot 804 and traffic 806. The central server can respondwith a hub transmission 808, which can contain responses to all thesatellite terminals that have transmitted over the period of a frame.The hub transmission 808 can include pilot and traffic signals 810, 812,as well as acknowledgements 814 and power settings 816.

In various embodiments of the invention, the acknowledgement informationcan be modulated. During each frame, the number of satellite terminalscheduled transmissions will be less than 256 (i.e., corresponding tothe number of orthogonal Walsh codes). As such, in the correspondingforward link frame, fewer than 256 acknowledgements (and 256 powercontrol signals levels) can be transmitted. A single (normal) Walsh codecan be assigned for acknowledgements and another single Walsh code canbe assigned for power control levels. Note that there are 512 coded bitswhere each of those is modulated by a normal Walsh code within eachburst. There can be two distinct categories of Walsh code basedspreading sequences: Normal Walsh codes (i.e., of length 256 for themost robust case) used to modulate each coded bit; and Long Walsh Codes,used to generate orthogonal sequences over the whole burst (i.e., oflength 512) where each bit applies to a symbol. To transmit a binaryvalue over the duration of a burst (e.g., ACK/NACK) a specific LongWalsh Code can be assigned to each satellite terminal. The mapping fromLong Walsh Codes to satellite terminals can be based on the returntransmit slot index. The 512 possible Long Walsh Codes are more thansufficient to support the number of satellite terminals which is lessthan 256 in number.

As the target Frame Error Rate (FER) falls below 1%, the expected ratioof ACKs to NACKs is at least 99:1. To conserve satellite power, it wouldbe beneficial to minimize the total energy needed to transmit thecombination of ACKs and NACKs. Received signals can be passed through amatched filter, synchronized in time and frequency, and correlated withthe known spreading sequences. The result can be viewed as a basebandequivalent 2-dimensional vector called a correlation vector.

FIG. 9 illustrates exemplary acknowledgement 902, 904 and power setting906 correlation vectors without noise or other impairments. To achieve adesired error rate in the acknowledgements, the distance in correlatedvector space between the constellation point associated with an ACK andthat associated with a NACK should exceed a minimum length. In oneembodiment 902, which shows an example with equal amplitudes for ACK andNACK modulation, this distance can be 2×D-an. One of the key drivers ofthe error rate can be the distance between the points, not theirlocations. The location of these constellation points in correlationspace is a degree of freedom, allowing the vectors to be moved such thatthe total associated energy can be minimized. For example, theassociated power may be 99×P-ack+1×P-nack, where P-ack and P-nack areproportional to the square of the amplitude of each vector. As there aremany more ACKs than NACKs, average power can be reduced by reducingP-ack and increasing P-nack. Average power is minimized when P-ack isclose to zero. In the case illustrated (with P-ack set to zero) by 904,the NACK-related correlation vector has twice the amplitude D-an;meaning that P-nack is 4 times what it would be if P-ack=P-nack as shownby 902. The average power required to transmit acknowledgements for case904 is about 4% of that required for case 902, which equates to areduction in power of approximately 96%. To achieve this performance,the decision threshold between the ACK and NACK related constellationpoints should be known. As the acknowledgements are transmitted in thepresence of pilot signals, the receiver can be configured to calibratethe location of the decision threshold.

The error rate for the acknowledgement process is typicallysignificantly better than for data traffic. For example, theacknowledgement process error rate can be lower than 0.1%. At the sametime, the error rate for NACKs can be traded against that foracknowledgements ACKs. This trade can be driven by the relative costs ofa mistake. For example, a NACK received as an ACK can result in failureto communicate the message, while an ACK received as a NACK can resultin an unnecessary retransmission (which would typically have lessimpact). According to various embodiments of the invention, theacknowledgement process can be implemented using existing physicalbearers, without specific changes to the physical layer design toimprove efficiency.

Initialization of communication between satellite terminals and thecentral server can be accomplished in a number of different ways. Forexample, scheduled satellite terminal transmissions can be used where apredefined time is established at which the satellite terminal wouldtransmit a fixed length message. A typical embodiment of this type canbe used in many different applications, such as, for example, regularutility meter readings. Another exemplary embodiment can usealarm-driven satellite terminal communications. In these embodiments,some event at the satellite terminal can initiate an exchange ofinformation. For example, opening a door can trigger an alarm that wouldbegin an information exchange. In still another embodiment, pagedcommunications can be used in which the central server initiates anexchange of information. One sample application of this type ofembodiment could be used to change parameter settings in the satelliteterminal.

Each satellite terminal can have a unique associated identity, denotedby a Mobile Device Identity (MDI), which can be a 64-bit value. Duringoperation, a satellite terminal can also be assigned a Temporary MDI(TMDI), which can be shorter, such as a 24-bit value. Duringalarm-driven communications the related satellite terminal will identifyitself, and for paged communications the satellite terminal can beidentified by the central server. This identification can be provided bythe TMDI. During scheduled transmissions, the satellite terminal can beaware of the transmission time and the central server can be aware ofthe identity of the satellite terminal that is configured to transmit atthe scheduled time. The central server can identify the satelliteterminal without having to read information from the content of thetransmission. In other words, identity information need not be includedin the transmitted information. For example, in a burst containing 112payload bits, the application-related information can be increased by27% by avoiding the transmission of 24-bit identity information. Inaddition, each satellite terminal can be configured to apply uniqueciphering to its transmitted data, providing another means of confirmingthe identity of a source satellite terminal.

When a satellite terminal powers up, it can acquire and synchronize tothe forward link channels of a satellite. This can be accomplished in anumber of ways. For example, with typical acquisition algorithms, thesatellite terminal can detect the presence of a pilot channel, which canbe used to determine estimates of the carrier frequency and timeslottiming. The start time of each timeslot can be resolved, but thelocation within each frame and the frame number are typically notdetermined by the acquisition algorithm. The BCCH can then be observedso that the frame boundaries can be determined.

FIG. 10 illustrates one exemplary BCCH payload structure 1000 accordingto various embodiments of the invention. The BCCH can use multiple knownWalsh codes, transmitted in a known sequence, while modulating thepayload information. By searching for correlation with the expectedpattern of Walsh codes, framing of the forward link can be resolved. Assuch, a separate synchronization channel is not needed thus savingsatellite power. As shown in FIG. 10, each BCCH burst payload canconsist of 128 timeslots 1002, each of which can contain four Walshcodes 1004 associated with four coded BCCH bits 1006. The boundaries ofthe timeslots can be resolved as described above. The same Walsh codecan be used for the 4 symbols of each timeslot. Over the 128 timeslots,16 different Walsh codes can be used. The Walsh codes can be arranged ina pseudo-random pattern that can be selected with the goal of maximizingthe distance between the correct framing and any offset of that framingby an integer number of timeslots. After establishing framing, thecontent of the BCCH can be received and the frame numbering can be readfrom system information.

Different satellite terminals can have different capabilities in partbecause applications associated with each satellite terminal may havedifferent requirements. For example, a mobile terminal, such as one usedfor tracking a vehicle may have different capabilities and requirementsthan a stationary terminal, such as one used for utility metering. Theparameters of protocols and other terminal characteristics establishedby the central server can depend on awareness of these capabilities.Additional differences may arise as the system evolves and terminalswith newer capabilities are introduced. However, because thecapabilities associated with satellite terminals in embodiments of theinvention can be mapped to their identities (MDIs), there is no need toexchange information related to terminal capabilities. When transmittinginformation, the formatting of data may depend on the associatedapplication, such as information related to electric meter reading orvehicular asset tracking. However, in embodiments of the invention,there is no payload overhead for defining field sizes, locations, etc.because the formatting of scheduled transmissions (and others) can alsobe mapped to terminal MDIs.

According to various embodiments of the invention, satellite terminalscan be configured to support applications that transmit data atpre-defined times based on regularly-spaced intervals, but where theprecise time of the transmission is not critical such as utility meterreadings. Other services, such as voice links, provided by a satellitecan involve concentrations of throughput at specific times of day, suchas during times of heavy voice traffic. Typically, satellite terminaltransmissions will be scheduled to avoid predicted busy hours. However,in some cases, satellite capacity may approach its limits due tounforeseen events. Under such conditions, scheduled transmissions can bereassigned based on parameters delivered via system information whichcan be read by the satellite terminals prior to transmission. Thisreassignment process, called scheduled transmission quietening, enablesdelaying of selected scheduled transmissions for a period of time. Whenrescheduling, a defined timeframe can be cleared of scheduledtransmissions and transmissions can be rescheduled over the followinghours. After conditions change, the system can return to normaloperation. Scheduled transmission quietening can be used to efficientlyenable management of satellite resources without individually changingthe transmission schedules of every impacted satellite terminal.

In order to implement scheduled transmission quietening in embodimentsof the invention, three system information parameters can be used todefine the real-time communication status. A scheduled transmissionquietening active flag (SI_quiet_flag) indicates that scheduledtransmissions should not be transmitted. This flag can be set to stayactive for a specified amount of time such as 2 hours. Additionalparameters are used to define the configuration of quietening. Oneparameter (SI_ELMT_quiet_period) can be used to define a period of time(the quietening delay) that is equal to or longer than the period ofquietening, where the parameter's 4-bit value is in units of 512 frames.A second single bit parameter (SI_ELMT_quiet_spread) can be used todefine whether the retransmissions are spread over 4 quietening delayperiods or 8 quietening delay periods. The selection of which of the 4(or 8) quietening delay periods to use for the retransmission can bebased on the Least Significant Bits of the terminal temporary identity(TMDI), which is a number known to both the terminal and theinfrastructure.

FIG. 11 illustrates an exemplary quietening process 1100. An operatormay initiate a period of quietening that can be applied to scheduledtransmissions at 1102. In doing so, the operator sets the quieteningparameters which are entered into the System Information broadcast inthe BCCH at 1104. For example, a period of 1.5 hours can be selectedduring which scheduled transmissions should be disabled (e.g., 9:00PM-10:30 PM). In addition, the quietening delay can be set (viaSI_ELMT_quiet_period), such as for 2 hours, and the number of delaysteps after quietened transmissions can be set (viaSI_ELMT_quiet_spread), such as for 4 times. Next a satellite terminalwill wake up at 1106. The satellite terminal then determines whether ornot quietening is currently enabled by reading the System Informationentry, SI_quiet_flag, at 1108. If quietening is not enabled, thesatellite terminal proceeds with its scheduled transmissions at 1110. Ifquietening is enabled and the satellite terminal has an assignment for ascheduled transmission during the quietening period, such as 10:05 PM,the satellite terminal can read the quietening parameters from thesystem information at 1112. The satellite terminal can then determinethe rescheduled transmission time, at 1114, based on the quieteningparameters. In order to do so, the satellite terminal can select anumber between 1 and the number of delay steps after quietenedtransmission parameter, which, in this example, is 4. A deterministicreference known to the central server, such as Least Significant Bits ofthe TMDI, can be used to selecting the number. For example, in thiscase, the selected number may have a value of 3 (i.e., between 1 and 4).The transmission delay can then be calculated by multiplying theselected number (plus 1 to include the quietened period) by thequietening delay. In this case, since the quietening delay is 2 hours,the calculated delay is determined to be 8 hours or until 6:05 AM. Aftercalculating the transmission delay, the satellite terminal goes back tosleep, at 1118, until the delay expires. At 1120, after the delayexpires, the satellite terminal wakes up and, at 1122, the rescheduledtransmission begins. It should be noted that the transmissions that havebeen delayed by the quietening process are transmitted with differentCRC masks thus enabling the central server to distinguish rescheduledtransmissions from regularly scheduled transmissions.

During scheduled transmissions, the central server can respond to eachtransmission with an acknowledgement and a power setting level. As therecan be a correlation between the purposes of these values (i.e., lowpower is more likely to lead to failed communications and a NACK), thevalues can be interpreted as a pair when deriving power changes. Forexample, the following table provides an exemplary correlation betweenacknowledgement and power setting level.

Power Acknowl- Control Action for Next Nominal Power Case edgement LevelTransmission (dB) Change (dB) 1 ACK +1 Lower power by P-am −0.5 2 NACK−1 Raise power by P-nm +1.0 3 ACK +1 Raise power by P-ap +1.5 4 NACK +1Raise pwer by P-np +2.0

The actual power level changes can be controlled via system informationor by terminal specific reconfiguration. A power control correctionsignal could be transmitted within a range relative to a pilot signal(e.g., if the pilot signal amplitude is +10 units, the power controlcorrection signal amplitude can vary in one dimension of a base-bandvector representation such as between −1 unit and +1 unit as shown by906 in FIG. 9). The power control correction signal may be transmittedwith a level anywhere in this range, indicating different requestedchanges to the satellite terminal's transmit power. The power changes inthe above-table could be scaled by the level of the power controlcorrection signal. That is, control scaling could be analog. Thisapproach is possible due to the presence of the pilot signal, whichenables calibration signal levels.

Error rates for acknowledgements should be lower than those for themessage payload. For power control, on the other hand, high error ratesare typically more tolerable, as (for example) any reception of a NACKcan cause an increase in subsequent transmit power levels, irrespectiveof the received Power Control level. In exemplary implementations, theenergy associated with transmitting a NACK might be 8 dB lower thantraffic energy, while that for Power Control might be 23 dB lower thantraffic energy.

In summary, the key features of a scheduled transmission (for the mostcommon scenario in which no errors occur) are:

-   -   A message with no overhead (i.e., all payload bits are        application-related) is transmitted,    -   No energy is used sending the ACK,    -   Power setting for future transmissions (if transmitted) is sent        at a low power level.

Assuming 1% FER, and that Power Setting levels are transmitted, theaverage power transmitted in the forward link responding to eachscheduled transmission could be ˜1.1% of that of a forward link trafficburst.

The link margin of the forward link can be increased by raising thepower transmitted at the satellite. At the same time, satellite power isa precious resource. By occasionally transmitting BCCH bursts at higherpower levels, a trade between satellite power and/or link margin, anddelay can be provided. As a satellite tends to be limited by the totalinstantaneous transmit power, it is typically advantageous to cycle theincrease in power from beam to beam. For example, by arranging beams ingroups of 16, the BCCH power could be increased in each beam for1-out-of-16 BCCH bursts. By identifying the pattern of higher power BCCHbursts to the satellite terminals via system information, thoseterminals can target their reception to the higher power bursts forcases when they note that their receivers are operating at or belowthreshold signal-to-noise ratio. This same capability can be applied tolower average satellite power while still maintaining nominal linkmargin.

In some circumstances, a satellite terminal may not be able to detectthe forward link signals, such as when the satellite is shadowed. If, atthe same time, a terminal user requests an emergency alarm, thesatellite terminal may be able to transmit a related emergency message.If GPS timing is available, the satellite terminal may use this as abasis for synchronizing its transmitter. If not, the terminal maytransmit with synchronization based on its local reference oscillator.In this case, consideration shall be given to the potential frequencyerror, and how it might impact neighboring channels or how it mightimpact compliance with any regulatory requirements. Emergencytransmissions may include information such as the identity of thesatellite terminal and its location. These transmissions may be repeatedat times defined for each terminal. The time between repetitions isknown to the central server, which may attempt to combine multipletransmissions to reduce the error rate and thus identify the satelliteterminal and its location.

In some circumstances, a satellite terminal's location may be ofinterest, under conditions in which the satellite terminal is unable tosuccessfully transmit. For example, after a valuable item with anattached satellite terminal has been stolen, operators at the centralserver may invoke an emergency page. The hub can be aware of the pagingreception time of a satellite terminal. Prior to reception, thesatellite terminal can wake up and attempt to acquire the forward linkchannels. During the time the satellite terminal is attemptingacquisition, the forward link signal levels may be raised to increasethe link margin for both acquisition and the page. Once the satelliteterminal receives the page, it can respond by transmitting a completeburst with known content at the maximum power level. This can befollowed by a separate burst containing the terminal's location. Theoperators may also suspend other traffic in the return link during thetime the satellite terminal is transmitting. This may increase theprobability that the satellite terminal can be contacted and willrespond.

Satellite terminals may switch between networks, which may be providedby different satellite operators, to provide, among other things,continuity of service in the event of a satellite failure. Support forthis flexibility may arise in the satellite terminal implementation,such as, for example, carrier frequency flexibility, and in the systeminformation, which may include definitions of existing networks as wellas parameters enabling future networks to be defined. In situations inwhich a satellite terminal is covered by multiple networks, the centralserver may direct satellite terminals to a specific network. The systeminformation may include information related to multiple networkoperation centers such as frequencies, chip rates, filtercharacteristics, etc. The satellite terminals may be configured withprioritized network preferences and/or the central server may beconfigured to redirect satellite terminals to different networks. As newnetworks come into existence, the system information may be updated todescribe these new networks.

System Information (SI) can be a set of parameter values that arebroadcast from a Hub to all terminals in a beam. In typical systems, SIcan be arranged in a number of classes, enabling efficient management oftransmission of the information. For example, information that changesrarely, such as descriptions of space relays, can be placed in a classwith other rarely changing information. The priority, and likelihoodthat parameters will change, can drive the duty cycle at which eachclass of SI is transmitted. Particular SI parameters may be repeated inevery BCCH burst, and some may not be repeated for many BCCH bursts.Some information may change at any time, and should be read before aterminal transmits, e.g., flags that can disable transmission. Aterminal that is about to transmit should read these flags, but may notbe required to learn of all the available space relays that areavailable. In another scenario, a newly registering terminal may gothrough the process of reading all the SI, including descriptions ofspace relays.

The System Information associated with scheduled transmission quieteningcan provide an exemplary case. In FIG. 11, a terminal reads quieteningparameters from the System Information 1106 and 1112. FIG. 16 shows thisprocess in more detail, where the quietening parameters are:

-   -   SI_quiet_flag; a 1-bit value in Class-1 System Information    -   SI_ELMT_quiet_period; a 4-bit value in Class-2 System        Information    -   SI_ELMT_quiet_spread; a 1-bit value in Class-2 System        Information

In preparation for a scheduled transmission, the terminal can read theClass-1 information 1602, which can be included in every BCCH burst.From the Class-1 information, the terminal can learn the value of theSI_quiet_flag (i.e., that quietening is requested). Given thisinformation, the terminal can be aware (a) that there will likely be asignificant delay before the transmission occurs, and (b) that it shouldread Class-2 information to determine the parameter settings for thequietening. The terminal, therefore, can proceed with reception of theClass-2 information 1610 and with determination of the values ofSI_ELMT_quiet_period and SI_ELMT_quiet_spread 1612. Note that theassignment of these parameters to Class-2 can be enabled by theavailable time for reading the content. In general, parameters can beassigned to the highest class number that enables the desired relatedoperation.

Embodiments of the invention can also be configured with securityfeatures such as authentication of each satellite terminal by thecentral server during registration, authentication of the central serverby the satellite terminals during registration, and/or ciphering of datatransferred between the satellite terminals and the central server toname a few. In one embodiment, these security features can beimplemented using a set of non-public keys that are stored at eachsatellite terminal and the central server. Compromise of the secret keysstored in a particular terminal would only impact that satelliteterminal. In other words, the keys stored in a particular terminal donot provide information related to other satellite terminals. Means foridentification of anomalous behavior by potentially-comprised terminalsmay be applied. For example, transmission from distant locations bymultiple terminals with the same identity could be flagged as apotential security threat.

Unlike in conventional systems, the security related processing inembodiments of the invention occurs at the central server rather than atthe hub. This approach provides enhanced security as secret keys neednot be moved to hub facilities and the list of temporary and permanentsecret keys for all satellite terminals can be maintained in onelocation. As embodiments of a system according to the present inventioncan be implicitly aware of the identity of every satellite terminal andall communications can pass through a single point and can be associatedwith specific owners, the motivation for compromising the system isinherently less than conventional systems.

Transmissions by satellite terminals can be prevented by the centralserver via the system information. In this way, it is possible to managesystem resources, such as power and bandwidth, when a space relayapproaches capacity. These controls typically apply at the time they areread by the satellite terminals. In other words, a satellite terminalmust read the system information within a specified period prior totransmission. Individual transmissions may be prevented based on avariety of things such as terminal class and/or communication mode.

In various embodiments of the invention, the maximum length of a mostrobust burst can be 1,024*128 (2¹⁷) chips, corresponding toapproximately 5.6 seconds at 23.4 kcps, with an information data rate ofapproximately 20 bps. By using shorter Walsh codes (in factors of 2steps), higher information data rates can be achieved. For example,rates of 40 bps, 80 bps, 160 bps, 320 bps, etc. can be achieved. Thelength of bursts can correspondingly be reduced with the informationcontent of each burst remaining fixed. Bursts can be structured tosupport different data rates. For example, forward broadcast controlchannels can operate at the most robust data rate. For forward trafficchannels and return link channels, bursts, configured during connectionestablishment can be configured for a factor of 2^(N) increase in datarate. For example, the number of timeslots in the burst can be reducedto 128/2^(N), the number of chips in the Walsh codes can be reduced to256/2^(N), the length and content of Gold codes can remain unchanged at1024 chips (a timeslot), and the number of coded bits per timeslot canincrease to 4×2^(N). Frame timing can be divided into sub-frames oflength 2^((17-N)). The hub can advertise the data rates of support forRACH, enabling the satellite terminals to select a supported rate. TheAGCH can use the same rate as the RACH, but may assign another rate forsubsequent communications.

In some situations, satellite terminals in an embodiment of theinvention may be aware of Global Navigation Satellite Systems (GNSS).These systems may provide reference timing signals that could be appliedas a reference for framing, etc. If satellite terminals are aware thatframing is based on GPS timing, the satellite terminal may determinetimeslot and burst frame timing, during acquisition, without having toderive it from the received signals. This can reduce the time needed foracquisition and thus reduce power. Terminals that are transmittingwithout receiving could also use the GNSS timing to transmit in specifictimeframes that could be pre-arranged. Additionally, the terminals coulduse the frequency reference as a basis for reducing the frequency errorin their transmission.

In some operating conditions, channels may be shared with legacyservices, such as those associated with other mobile satelliteapplication like voice or packet data communication. This mode ofoperating is typically applied when the traffic volume is light (e.g.early in the deployment of a system or in beams that contain a smallterminal population). In one embodiment of the invention, the sharedchannel can be a control channel in the legacy system, in which the dutycycle of forward link transmissions is approximately 25%-50%. The legacychannels can operate with Signal-to-Noise Ratios that are 25-30 dB abovethat needed by embodiments of the subject invention. For example, legacychannels can require Ec/No=0 dB to 5 dB, where Ec/No is the ratio ofenergy in a transmitted chip (or symbol for systems without spreading)to the noise power spectral density. As such, the same forward linkchannel can be used to simultaneously transmit the legacy signaling andthe spread signaling associated with embodiments of the subjectinvention. If needed, the power used for transmission of the legacysignals can be increased (typically by a small factor) to maintain theperformance of the legacy system. Reception, in the forward link, ofbursts associated with embodiments of the invention can be achieved ifthe level relative to the legacy transmissions provides sufficientSignal-to-Noise Ratio, (i.e. Ec/(Io+No) where Io is the interferencepower spectral density associated with the legacy waveforms. In thereturn link, the legacy system can use RACH transmissions with low dutycycles. The transmissions associated with embodiments of the inventioncan also be transmitted with low duty cycle. Transmissions associatedwith embodiments of the invention will typically have lower power thanthe legacy RACH transmissions, so they can have a low impact on the RACHerror rate. As the legacy RACH transmissions have low duty cycle,relatively short burst lengths, and power levels that don't necessarilyprevent reception, transmissions associated with embodiment of theinvention can have reliable performance. As the performance of the linkscan be different during periods when the channel is shared with legacyservices, operation may be improved if the terminals are aware they aretransmitting on shared channels. The broadcast system information can beused to inform the terminals that they are operating on shared channels.

It will be recognized that while certain aspects of the invention aredescribed in terms of a specific sequence of steps of a method, thesedescriptions are only illustrative of the broader methods of theinvention, and may be modified as required by the particularapplication. Certain steps may be rendered unnecessary or optional undercertain circumstances. Additionally, certain steps or functionality maybe added to the disclosed embodiments, or the order of performance oftwo or more steps permuted. All such variations are considered to beencompassed within the invention disclosed and claimed herein.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the invention. Theforegoing description is of the best mode presently contemplated ofcarrying out the invention. This description is in no way meant to belimiting, but rather should be taken as illustrative of the generalprinciples of the invention. The scope of the invention should bedetermined with reference to the claims.

Although the invention is described above in terms of various exemplaryembodiments and implementations, it should be understood that thevarious features, aspects and functionality described in one or more ofthe individual embodiments are not limited in their applicability to theparticular embodiment with which they are described, but instead can beapplied, alone or in various combinations, to one or more of the otherembodiments of the invention, whether or not such embodiments aredescribed and whether or not such features are presented as being a partof a described embodiment. Thus, the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. As examples of the foregoing: the term “including” shouldbe read as meaning “including, without limitation” or the like; the term“example” is used to provide exemplary instances of the item indiscussion, not an exhaustive or limiting list thereof; the terms “a” or“an” should be read as meaning “at least one,” “one or more” or thelike; and adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known” and terms of similar meaning should not be construedas limiting the item described to a given time period or to an itemavailable as of a given time, but instead should be read to encompassconventional, traditional, normal, or standard technologies that may beavailable or known now or at any time in the future. Likewise, wherethis document refers to technologies that would be apparent or known toone of ordinary skill in the art, such technologies encompass thoseapparent or known to the skilled artisan now or at any time in thefuture.

The presence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent. The use of theterm “module” does not imply that the components or functionalitydescribed or claimed as part of the module are all configured in acommon package. Indeed, any or all of the various components of amodule, whether control logic or other components, can be combined in asingle package or separately maintained and can further be distributedin multiple groupings or packages or across multiple locations.

Additionally, the various embodiments set forth herein are described interms of exemplary block diagrams, flow charts and other illustrations.As will become apparent to one of ordinary skill in the art afterreading this document, the illustrated embodiments and their variousalternatives can be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

Moreover, various embodiments described herein are described in thegeneral context of method steps or processes, which may be implementedin one embodiment by a computer program product, embodied in acomputer-readable memory, including computer-executable instructions,such as program code, executed by computers in networked environments. Acomputer-readable memory may include removable and non-removable storagedevices including, but not limited to, Read Only Memory (ROM), RandomAccess Memory (RAM), compact discs (CDs), digital versatile discs (DVD),etc. Generally, program modules may include routines, programs, objects,components, data structures, etc. that perform particular tasks orimplement particular abstract data types. Computer-executableinstructions, associated data structures, and program modules representexamples of program code for executing steps of the methods disclosedherein. The particular sequence of such executable instructions orassociated data structures represents examples of corresponding acts forimplementing the functions described in such steps or processes. Variousembodiments may comprise a computer-readable medium including computerexecutable instructions which, when executed by a processor, cause anapparatus to perform the methods and processes described herein.

As used herein, the term module can describe a given unit offunctionality that can be performed in accordance with one or moreembodiments of the present invention. As used herein, a module might beimplemented utilizing any form of hardware, software, or a combinationthereof. For example, one or more processors, controllers, ASICs, PLAs,PALs, CPLDs, FPGAs, logical components, software routines or othermechanisms might be implemented to make up a module. In implementation,the various modules described herein might be implemented as discretemodules or the functions and features described can be shared in part orin total among one or more modules. In other words, as would be apparentto one of ordinary skill in the art after reading this description, thevarious features and functionality described herein may be implementedin any given application and can be implemented in one or more separateor shared modules in various combinations and permutations. Even thoughvarious features or elements of functionality may be individuallydescribed or claimed as separate modules, one of ordinary skill in theart will understand that these features and functionality can be sharedamong one or more common software and hardware elements, and suchdescription shall not require or imply that separate hardware orsoftware components are used to implement such features orfunctionality. Where components or modules of the invention areimplemented in whole or in part using software, in one embodiment, thesesoftware elements can be implemented to operate with a computing orprocessing module capable of carrying out the functionality describedwith respect thereto.

Furthermore, embodiments of the present invention may be implemented insoftware, hardware, application logic or a combination of software,hardware and application logic. The software, application logic and/orhardware may reside on a client device, a server or a network component.If desired, part of the software, application logic and/or hardware mayreside on a client device, part of the software, application logicand/or hardware may reside on a server, and part of the software,application logic and/or hardware may reside on a network component. Inan example embodiment, the application logic, software or an instructionset is maintained on any one of various conventional computer-readablemedia. In the context of this document, a “computer-readable medium” maybe any media or means that can contain, store, communicate, propagate ortransport the instructions for use by or in connection with aninstruction execution system, apparatus, or device, such as a computer.A computer-readable medium may comprise a computer-readable storagemedium that may be any media or means that can contain or store theinstructions for use by or in connection with an instruction executionsystem, apparatus, or device, such as a computer. In one embodiment, thecomputer-readable storage medium is a non-transitory storage medium.

What is claimed is:
 1. A communication system, comprising: at least oneterminal; at least one satellite which creates a beam having a beamshape that enables communication with the at least one terminal when theat least one terminal is located inside the beam; at least one networkinfrastructure in wireless communication with the at least one terminal,the at least one network infrastructure having an information elementwhich includes beam shape information representing the beam shape;wherein, the at least one terminal receives the information element fromthe at least one network infrastructure and calculates the at least oneterminal's initial transmit power based on the beam shape information.2. The communication system of claim 1, wherein the information elementalso includes scheduled transmission information and wherein the atleast one terminal is configured to communicate with the at least onenetwork infrastructure by sending a burst comprising a message at apre-scheduled time such that the at least one network infrastructure canderive a terminal identity for the at least one terminal by comparingthe time of the burst with the scheduled transmission information in theinformation element without having to include terminal identityinformation in the message.
 3. The communication system of claim 1,wherein the beam shape information describes the beam shape in terms ofgain as a function of spatial location formed by a transmitter of the atleast one satellite.
 4. The communication system of claim 1, wherein thebeam shape information describes the beam shape in terms of gain as afunction of spatial location formed by a receiver of the at least onesatellite.
 5. The communication system of claim 1, wherein the beamshape information describes the beam shape in terms of gain differencesbetween a transmitter and receiver of the at least one satellite as afunction of spatial location.
 6. The communication system of claim 1,wherein the beam shape has a cross section corresponding to a definedfunction.
 7. The communication system of claim 6, wherein the definedfunction is a sinc function.
 8. The communication system of claim 1,wherein the terminal determines an estimated terminal position based onthe beam shape information.
 9. The communication system of claim 1,wherein the terminal determines an estimated terminal position based oncorrelating signal-to-noise ratio measurements on the beam and at leastone neighbor beam neighboring the beam.
 10. The communication system ofclaim 1, wherein the terminal calculates an achievable information datarate of transmitted bursts based on the beam shape information.
 11. Acommunication system, comprising: a terminal; a satellite which createsa beams having beam shapes, the beams including a camped beam and atleast one neighboring beam which neighbors the camped beam, the campedbeam enabling communication with the terminal when the terminal islocated inside the camped beam such that the satellite communicates withthe terminal using a forward link and the terminal communicates with thesatellite using a reverse link; network infrastructure in wirelesscommunication with the satellite and the terminal, the networkinfrastructure having an information element which is sent to thesatellite and which is broadcast by the satellite along with systeminformation, the information element including scheduled transmissioninformation and beam shape information representing the beam shapes;wherein, the terminal is configured to: wake up at a pre-scheduled time;read system information broadcast by the satellite; read the informationelement; derive a location estimate of the terminal; determine a reverselink transmit power for the terminal based on the beam shapeinformation; determine an information data rate for the terminal basedon a threshold signal-to-noise ratio for the reverse link; andcommunicate with the network infrastructure by sending a burst at thedetermined reverse link transmit power and information data rate, thecommunication comprising a message at a pre-scheduled time such that thenetwork infrastructure can derive a terminal identity for the terminalby comparing the time of the burst with the scheduled transmissioninformation in the information element without having to includeterminal identity information in the message.
 12. The communicationsystem of claim 11, wherein the beam comprises a camped beam and thesatellite further creates at least two neighboring beams which neighborthe camped beam, the at least two neighboring beams having beam shapes,the information element further including beam shape information for theat least two neighboring beams; and wherein, deriving a locationestimate further comprises obtaining a signal-to-noise ratio for thecamped beam and the at least two neighboring beams from correlations andmatching the obtained signal-to-noise ratio for the camped beam and theat least two neighboring beams with the beam shape information to obtainthe location estimate of the terminal.
 13. The communication system ofclaim 11, wherein the beam shape information describes the beam shape interms of gain as a function of spatial location formed by a transmitterof the at least one satellite.
 14. The communication system of claim 11,wherein the beam shape information describes the beam shape in terms ofgain as a function of spatial location formed by a receiver of the atleast one satellite.
 15. The communication system of claim 11, whereinthe beam shape information describes the beam shape in terms of gaindifferences between a transmitter and receiver of the at least onesatellite as a function of spatial location.
 16. The communicationsystem of claim 11, wherein the beam shape has a cross sectioncorresponding to a defined function.
 17. The communication system ofclaim 16, wherein the defined function is a sinc function.
 18. Thecommunication system of claim 11, wherein a perceived signal-to-noiseratio of a forward link pilot signal is used in determining the reverselink transmit power.
 19. The communication system of claim 11, wherein aparameterized power increment provided by the network infrastructure isused in determining the reverse link transmit power.
 20. Thecommunication system of claim 11 wherein a long-term estimate correctingfor perceived differences in forward and return link gains is used indetermining the reverse link transmit power.
 21. The communicationsystem of claim 11 wherein a parameterized value representing a gaindifference between forward and return link gains at the satellite isused in determining the reverse link transmit power.
 22. Thecommunication system of claim 11, wherein a parameterized constantproviding an offset associated with a link budget is used in determiningthe reverse link transmit power.